What I do is hire a merchant, it's like everyone in your party has expert merchant if they have 2 on the skill points in merchant. The factor will give the party more gold when looting chests. The people reset, so if you don't find what you want to hire save and reload. Right click on the people to see what they do for the party.

Air is the most powerful magic tree because no monsters have resistances against it. Water is great for transporting around the world. Horseshoes give skill points.

Kill first, then heal, and open chest :) At low levels (sub20) sometimes you might get total party kill from specific chests (like those in Mire of the Damned), but some save-reloading + Protection from Fire/Elec/etc. buffs should let you survive. Disarm Trap becomes obsolete as soon as party gets access to Telekinesis spell (which can happen as early as your first visit to Free Haven), which allows to open all chests from long range (and can be used to open at least 2 very good chests in otherwise inaccessible places).

From what i also heard, Telekinesis could also be used to bypass Perception check in one of storyline Baa Temples. I didn't check if it works in that Temple myself when played through it, but Perception at 4 Expert allows to find items from all Skull Piles. Gold is much more important in MM 6 than EXP, so getting Perception could still be worth it.

Especially early in the game, I found it easier to kill monsters out in the open, keeping my distance, attracting only a few and using bows and moving (especilly in Iron Fist, where there are a lot of ranged attackers). Keep a check on the rythm with which your opponents shoot and turn as they stop or you'll miss, then start moving again as they shoot (also very effective against archers and dragons later in the game).

Temple of Baa probably is the most difficult dungeon that close to the castle, though I think some of the enemies in Dragoon's Caverns hit harder. I think the most important thing here is perseverance. I've also notice taht my characters hit more often once they've gotten used to an enemy, makng the first time you meet, say, a skeleton an endeavor of frustration becaue you just don't hit anything! Finding ways to avoid getting hit (again, use your ranged attacks. I always make all my characters experts in bow as soon as possible and your sorceror should definitely know Fire Bolt. Quick spell is your friend <3 ) while your characters learn the new enemy is really useful. There are ways you can hie around corners, especially if you have longer reach, and such little cheats. Hiding around corners is my favourite when battling magic users in dungeons.

You say you have trouble with money in the beginning. Honestly, if I wre you, I'd stop buying weapons and armour and magic paraphenalia in stores unless absolutely necessary, because you will fnd much better stuff afield. By raising one character's perception and luck levels, for example, and sing him/her to loot corpses, you raise your chance of finding items as well as gold and in Iron Fist you have an entire field of lizards, on whom you can find bows. I noticed someone here scoffed at levelling in perception, but if your money's tight, it's definitely advantageous. Also merchant. If you don't want to waste skill points on all your characters for this, just choose one and have them trade all your items. It's true that later in the gam, levelling will become extremely expensive and then it's good to have all merchants, but at this point, you'll want to prioritise.

I was more referring to the chests in Blackshire and Dragonsand, those absolutely will one shot a low or even a mid level party. I never really bothered with telekenisis because I generally don't bother with mind magic aside from remove paralysis.

Actually, enemy's chance to drop loot are set in stone and no stat can change it. Chests' contents are generated once you enter zone for the first time.

Sometimes you might notice that you can loot some chests twice, but it isn't really double-looting chests and has no connection to perception or luck, it just hadn't room to display all its contents first time (also advice: double check all chests).

All this is proven by Russian fans of MM VI -VIII.

Perception is only useful for treason quest (can be done with Telekinesis too) and skull piles at 4 Expert. It has chance to save you from chests' traps, but Telekinesis still outdoes it, thus Perception above 4 Expert is completely useless.
By the time player can enter Blackshire and Dragonsand (assuming he is playing normally, without cheesing, Blackshire and Dragonsand aren't really low-mid lvl zones) he should have some spare money to buy Telekinesis. Some thousands gold for Telekinesis, which player can get back rather quickly, versus quite limited skill points (and you need good investment in Disarm Trap to disarm those chests)?
Edit: you can actually get money back for Telekinesis book very easy. There is very good chest located off-limits in Paradise Valley, which can only be opened with Telekinesis.