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.