FWIW , I still have the original BG game and discs as well. Agreed, it is a PITA to install these days, which is why I highly recommend the BG Enhanced Edition from Steam. Not only is it less of a hassle, it has better UI, Resolution, more quests, and characters, but perhaps also more importantly it's not so impossible to connect to other players any more for multi-player. It was such a nightmare to play with more than 1 person back when it came out. My wife and I played through the EE without a hitch at all.
I can't imagine how long it would take to do everything there is to do in the games, so much of what becomes available to do depends on the choices you make...
One of the reason I like the series so much is that the dungeons literally do feel like dungeons, full of peril, traps and you never know what's around the next corner...not too many games can get that feel just right.