Hello there my fellow PPC brother. I'm currently working on a similar type game now. With a small 5-10 minute demo coming out next week due to the fact I've got Jam deadlines. I've learnt from many of my shortfalls and gone for a more bare bones approach. At this stage I think this new game should run on higher end G3s. The idea is that nearly every machine capable of running osx 10.4 will run it. Most G4s should run it no worries (I think). I've only got a high end g4 to test it on.
I've never played Baldurs Gate. I've played Icewind Dale and never made it past the Vale of Shadows. I've never played D&D in real life. Not super knowledgeable about the rules and those 2nd edition rules are even more confusing!