Never fully and serioulsy played through this game. I want to go through the whole thing on this playthrough so I am looking for the best mod setup for a blind playthrough.

Also I would like to know the ideal party size - mainly to avoid the game becoming a cakewalk due to high amount of party members ( I read around that 5 is a sweet spot ?)

If you're doing it blind go without ANY mods on your first playthrough, so you can see what the game is all about without fan based content. Go with mods AFTER your first try. Party size is up to you and down to you setup and play style. Go with the default.

Thanks. I should still go for bugfix mods right ? Using temple+ with vanilla settings?

You could, but you should be aware that Temple+ is a game engine extension that allows otherwise impossible things to happen in the game. If Co8 and/or Temple+ have ONLY bugfix options, go for it.

If you are an absolute purist, by all means use vanilla ToEE.

Otherwise I refer you to the Temple+ changelog so you can make an informed decision:

https://rpgcodex.net/forums/index.php?threads/temple-changelog.99319/

I found my starting party of 5 was slightly reaching level 10 by the time i was nearing the elemental nodes in the temple. Of course my cleric/mage were behind due to crafting items, but my other 3 party memembers reached level 10 with more of the game to go. The cleric and mage after crafting all the items reached level 10 inside the elemental nodes.

I didn't farm areas with waiting/random spawn either. So, just based on my last playthrough, i would say a good party size would be 6 people. MAYBE 7 if your a vet and do a lot of the quests, etc. but id think just 6 people would be fine.

Warrior, cleric, mage, thief, maybe a leader thief warrior with all the diplomatic skills, and I would do another mage. Magic missiles and fireballs really make many areas very easy. My thief and thief/leader both were dual welding dagger warriors. That way i could spread out the thief skills and pick warrior feats for them to help out in the combat area. Both were humans to get extra feat and skill points. One thief for thieving, one thief for diplomacy and negotiations. Worked out great. I went daggers because it was easy to get the weapon focus/specializations, dual weapons, etc for just 1 weapon type, and really not a huge difference with a shortsword vs a dagger, so dual daggers worked out just fine.

The first time playing i didn't pick up combat skills on my thief/leader, and regretted it. He wasn't really useful in combat at all except for using wands my mage made for him. Not many magic bows in the game to make him a good archer even though i picked up archer skills, so he was just "there" much of the time. Much better the 2nd time around with him also as dual daggers and able to fight in melee. Ignored archery all together. Ick in this game.

So as to the topic, id say 6 party members should work out well based on my experience leveling in the temple and near endgame. Don't be afraid to have your clerics and mages picking up the make wonderous and armor/weapon feats, you can outfit everyone with great stuff. Both on both of them to spread out the experience loss. And pump out those great gears. With CO8 you can pick up a 2nd mage to help out also. Dual mages with spells (magic missiles/fireballs) along with 2 rogues who can use wands the mages/clerics make who can also pump out magic missiles/fireballs) when needed.

My first play-through ever was using only the vanilla game (ie. no Co8 mod), and it is doable, but quite a hair-pulling experience. Be aware that some bugs are serious ones... there are bugs in the non-modded game that can cause unrecoverable crashes and iirc there was even a bug that caused data corruption in saved games. So if that bothers you that somewhere 3/4 of the way through, you may have to restart the whole campaign, I would recommend at least installing Co8 and run it in 'vanilla' mode.

In my first game, I spent hours tailoring my party of 6 during PC creation, chose a CN party, and they all got killed in the pre-Hommlet intro encounter because I didn't understand damage resistance. Just saying, TPKs are part of the game, and just walking outside of town can get you killed...

Thus now I always go with 1 PC at start, then flesh out the party with the many hire-able NPCs available throughout the game. It gives the Hommlet early game (and later Nulb) some sense of purpose if you are looking to actively recruit and have some slots open.

There are only 6 'active' slots, so the more PCs you bring in the original party, the less options you have for adding NPCs later.

SPOILER ALERT (kinda) ABOUT MICROMANAGING NPCs:
Be aware that in the vanilla game, NPCs joined to the party fill up their inventories with personal loot and never let you sell it, eventually becoming encumbered and useless. But you can get around this by filling their inventories with arrows or goodberries or something so there are no empty slots in their backpacks.

Also, Charm Person and other Enchantment school spells rock in ToEE... just saying.