Weeelll...I do have the option of rotating through a variety of race/class enemies as was done in the Goldbox games (most prominently Treasures), with 'special' enemies for flavor at big fights. I'm personally not fond of the serial mod, though I realize we are limited by the 36 dungeon limit (there was no way Ray Dyer was going to make the Realm a single mod). But...life is about compromises.
One thing I did want to do is have the treasures scattered throughout the game held by enemy adventuring parties, so you get the Short Bow+1 and the 20 arrows +1 by fighting a character with it. These would probably be unique enemies. There are about 70 discrete 'treasure points' in POR by my count, and I might be able to reuse some enemies for some of the items that popped up more than once like the Short Bow +1 or the Chain Mail +1.
Pool of Radiance also has its own race/class enemies like '3RD LEVEL FIGHTER', who I associate with POR just as I associate the Red Bit of Moander and the Blue Bane Minion with POD, or the Skel Warrior with DKK. I could use them to round out parties, and they will probably be necessary anyway as the party should wind up fighting New Phlan's guards eventually.
A challenge is going to be keeping the fights interesting. Usually Goldbox games had a mix of humans (cast Hold Person and Stinking Cloud), humanoids (cast Sleep, or fireball/stinking cloud for giants), undead (turn or fireball), and monsters (fireball, or combat if immune). (In Buck Rogers, this divided up nicely into humans, robots, and monsters, each of which had its own tactics and preferred weapons.) A humanoid party should still be able to encounter undead in the graveyard and Cadorna Textile House, or monsters in the wilderness (though some of the more obscure ones are going to go), but there will be a strong human/demihuman presence due to the premise of the game. Any suggestions?