Following the suggestions to build a mage character that will have the best dialogue options and have the best chance at getting the best ending i'm almost decided on these stats:

Wis 18
Int 17
Cha 13
Con 9
Str 9
Dex 9

I'm almost considering taking a point away from Cha and dropping it into Con for a Con of 10 as i'm a bit uncertain about being able to survive the default difficulty in this game. On the other hand, starting with a Con of 10 only adds 2 more hit points which isn't a huge difference. Any suggestions?

Increased Con doesn't really start to pay off until you get it to significantly higher levels (16+). You'll also start off with Morte as your companion, who is an incredible tank in combat. Lastly, keep in mind unlike the traditional 2e rule system, where your stats are fixed at character creation, TNO gets to raise his stats every time he gains a level in his highest class, so you'll be able to boost your stats quite a bit as the game progresses. Taking all of that into consideration, I'd say your starting choice of stats works quite well and would recommend going with it without any changes.

I actually would recommend dropping a point out of WIS and a point out of INT and putting them into one of the physical stats, probably DEX. You get a bunch of free WIS boosts throughout the game, so 18 is kinda unnecessary as a starting stat. As is, you could put zero points into WIS at level-up and still have "wasted" WIS boosts by the end of the game, as the cap on abilities is 25. As a mage, you'll similarly get several INT boosts, including one from a mage-only tattoo that you WILL want to have equipped. WIS is the most important stat in the game, but it's not really necessary to have it THAT high from the beginning, as none of the really challenging dialog options show up until a lot later, and you really won't miss the extra 2% XP.

Even as a mage you're going to want DEX and CON eventually, and STR doesn't hurt as you can often just knife enemies and save your spells for later. Having a half-decent DEX also helps with several early encounters when you're trying to grab someone or something. CON is pretty important, but it's retroactive so you don't really need to worry about boosting it right away.

You can get a total of +7 to wisdom through the game if you take all the right dialog options (although two of those are right at the end). Wisdom also boosts experience gained, so it's good to have it high right from the start (at 16 you'll only be getting a 10% bonus, if you kick it up to 20 you're getting a 20% bonus, and all the way up at 25 you're getting a 35% bonus). TNO also has no level cap, so the extra experience gained by having the extra wisdom early can actually earn you more stat points overall, making up for one or two "wasted" points by hitting the cap of 25 early. There are also some dialog checks requiring reasonably high wis and int fairly early in the game, so it's good to start those out high. And for int boosts you can only get +4 over the course of the game, and that's including both of the mage specialization bonuses.

Sounds good, I just had to wonder about CHA as i've heard suggestions from some saying it isn't as important.

CHA is important as is INT or WIS.
In most cases CHA will alow you to avoid fights and get more money, which is very usefull(Buying Tatoos mostly.) at the start of the game.
And 13 CHA is a great way to go since you can pass most of the CHA dialog options at the start.
Keep in mind if you say, take away 1 point from one stat and add it to an other stat, that won't do you much good since 10 points in any stat is not worth of anything, and you just ruind the stat that could get you some cool stuff.
13 is where you see the benefits in any stat.
So ceep those stats as it is and enjoy the game.

Also maybe this will help.
SPOILERS!!
but not major, it's a guide to a good start.
http://www.gamespot.com/planescape-torment/forum/starting-stats-44198188/
The last post there is worth the read.

That sounds pretty good, I think i'm ready to tackle my very first Infinity Engine game now.

Thank you all for the advice. :)

10 instead of 9 con only grants you 2 extra hitpoints and lets you regenerate 1 HP every 55 instead of every 60 seconds.
Con is an extremely powerful combat stat but the difference between 9 and 14 is relatively small, the higher it is the more you benefit from raising it by one.
So either plan raising it high or ignore it totally, if you plan raising it I recommend starting with 14 since you get 2 extra HP per con point which you don't get when you raise it later.

If you have 14 con and feel wimpy you can simply raise it and feel considerably stronger immediately, if you have 9 con and feel wimpy you have to spend 6 level up stat raises until you feel a difference so decide at the start which way you're going.

Starting with 18 wis is fine. You won't get to the cap.

I wouldn't start with more than 16 int, there's no real benefit in having more unless for mages who have a stat check for 18 but there's equipment to raise it and stat raises during the game, so even the 2 HP from 10 con would help more.

12 Charisma is enough to avoid all fights on the mortuary ground floor. Mages can simply spam "friends" spells to get it to 25 temporarily even if they have 9.

I'd either trade one point from int to cha or start with 14 con, 16 int, 15 wis and 12 cha and raise wis at the next level ups until it's 19. Afterwards put points into con if you feel wimpy or into cha if not.

But your character stats are fine even unchanged and since I strongly recommend avoiding spoilers it's only guessing in which direction you'll go and which stats will grant you the best game playing experience. Wisdom affects the stat checks more than all other stats together and even with low wisdom you can have a good experience.

Personally I don't like playing with low con since I want my character to charge into battle instead of hiding behind party members and don't want to wait so long to regenerate or walk to the few resting places if injured.

As a mage, you actually get +8 wisdom due to specialization, and with the level 12 mage specialization tattoo (which you should wear at all times) you'll have a total of +8 intelligence too.

Personally I just find that PST is a lot less irritating in the early stages if you don't neglect your physical stats completely, and 17 WIS is enough for anybody to start with. The 2-3% xp you lose throughout the game ends up being fairly irrelevant, but if it bothers you then you can always boost it as much as you like as you level up.

Everyone be aware that this thread is named "Starting stats for a first time player" and not "dialogue powergaming advice for a walkthrough hugging robot".
PST was made for roleplaying and writing one's own story, unspoiled without using walkthroughs, reloading dialogues or doing similar stuff.

And if you're roleplaying instead of reverse engineering every little bit of the game you definitely won't get all stat upgrades but you'll definitely get the far better gaming experience nevertheless.

If you're crazy for maxing stats simply fight respawning monsters until you've gained enough levels to raise all stats to 25 or simply use a cheat program, but don't let it spoil the game for you.

The link by TheEvilAlex contains heavy spoilers and should be marked as such and I really don't recommend any newbie following this thought experiment.

Also want to mention, I'm at the start and I have no problem beating the crap out of most things in the game with the lowest CON, STR, DEX, so there's that.

So you recommend following a guide which tells how to walk around after many level ups with 25 int, 25 wis and 23 cha just for the sake of the numbers looking good.
7 stat points are wasted for int and 7 stat points are wasted for cha (there's barely any benefit of more than 18/16) which could be used for something useful (there are also str,dex and con checks outside combat) and it's not the best idea to raise int and wis to the cap just before getting the opportunity to raise int by 1 and wis by 3.

Good gracious... this is one game where it's actually possible to roleplay to a fair degree. Pick any stats you want, and you'll do well. It really doesn't matter much. Okay, it's nice to have good wisdom to get the most out of the game via dialogue, but beyond that anything goes. There are enough meta-gaming games out there, we don't need to do that crap with Planescape too.

As I said, I am only at the start of the game and it worked for me so far.
But you do have a point and following this guide all the way will get you waisting some of your points so I don't recommend you do that, and I also never intended to do that.
But to me it looks like going to the level 6 mage part is not a bad idea.

You are spoiled which makes a huge difference. You already know where the easy quests are, how to get equipment, experience and other stuff to make you stronger without effort and can easily avoid or delay the challenging fights.

Without spoilers or a walkthrough to hug it's different. If you already know where exactly which things are it's no problem running from location to location but it's different if you explore the areas yourself. Exploring unknown areas doesn't work well with monsters running after you, if you happen to get close to thugs or monsters and they decide to attack you you have to fight them. And if you fight them you will get injured. And to get healed you'll have to wait for the slow HP regeneration or spend money you don't have for healing stuff or walk to a resting place you first have to find or die.

If you're spoiled combat is easier, but if you're using a walkthrough you can simply dump int and cha and raise it temporarily on the few occasions you get a benefit and create a powerful character instead.

I'd even say an unspoiled first time player who creates a high wis character will experience more if he has high con instead of int or cha since he won't run away from or avoid attackers.