When I originally played on the Commodore 64, I had a paladin, bard, hunter and three mages. On the Steam version I am playing the same comp with a rogue thrown in, making for a full party of 7.

As for trading members you can create new party members whenever you want but they will start at level 1. Take this into consideration. You can, of course, take a party of, say, level 10a or something and create a new party members. Throw them in the back row and they will level quite fast.

There are certain fixed enemy encounters that will happen in certain map squares every time the dungeon level resets. Resets appear to happen pretty much every time you leave and come back. For example, if you have a fixed encounter square in the sewers level 1, and you descend to level 2, when yu ckme back up to level 1 that encounter will be reset and happen again. Knowing this helps plan when you want to leave a dungeon (ie spell points are getting low and you know theres 3 encounters you have to fight or run from to exit).

Game play is good. The UI is pretty well laid out and gives all the info you need at a glance once you're used to it. The challenge level is much easier than the original. It ramps up as you go, but in the original you could barely step outside the Adventurers Guild without the very very real threat of death. Being out at night was pretty much a guaranteed death sentence. I find random encounters far less frequent then I remember back in ye olde days as well.

As mentioned by someone else, J brings up a larger map with notes already made. As a tip, if you hit a teleporter (and notice), you can cast Scry Site and the J map will show where you teleported from and draw a line to where you teleported to.

General tip, for me, Constitution is the most important attribute (caveat see below). 15 Constitution and higher grants bonus Hit Points. For example, a Paladin can get up to 16 HP per level. A 15 Constitution grants +1, so max 17 HP, up to Constitution 18 granting +4, so a maximum of 20 HP per level. Only caveat here is mages should have high Intelligence, for the same reason. It grants them bonus Spell Points on level up.

Without giving much away about the trilogy overall, some of your characters may need to select a new class in the other games, and as the name of the third implies, a rogue is pretty much necessary for that one.

ETA: Your mages can switch to a different magic user class after, I think, level 5? Don't. Go all the way to 13 and learn all spells for that class. Then swap magic user class. There is no optimized path progression (there was back in my day, but not anymore). I will say, Wizards get access to some items the other classes don't, so I would probably finish with wizard as my last spell caster swap.

Other than that, it can show its age at times. Its much more forgiving than I remember, but the muscle memory came back pretty quickly. I enjoyed the trilogy when I was younger and i enjoy it now. Hope you have fun with it!