You should really check
Red 6's site out Matthew - it's one of the best reference sites on the net. He's got a whole page dedicated to all of the characters hanging out out Jabba's pad, right down to the most obscure and inconspicuous ones that you probably never even saw on the screen.
But Matt, are you only going to be using vintage figures in this diorama, or modern era figures as well? Obviously the vintage ones will cost you a pretty penny - especially EV-9D9 and Yak Face, whereas most of the modern ones were peg warmers that can still be had for relatively cheap still. You'll have to definitely go with the vintage Jabba for the time being though, since there's no modern counterpart that even comes close (though a nice one is rumored to be coming...)
You'll also get a much greater character selection if you go with the modern era, which will include several figures that weren't available in the vintage line, like Ephant Mon, Slave Leia, Oola, Ishi Tib (wrong outfit though), B'omarr Monk, all the Special Edition dancers (3-pack) and band members (2-packs), etc. Not to mention the modern figures generally have better, more accurate sculpts and paint jobs of course...
If I recall correctly, the only vintage figure from Jabba's Palace yet to be remade was Klaatu, so you might have to track him down from the vintage line as well, though he shouldn't cost too much for a loose one. Good luck! Can't wait to see the finished diorama!
And for those who may have missed the Fish's previous thread like this one -
recreating the Arena battle, asking for tips on a complete and authentic Arena diorama, let me tell ya', the thing turned out pretty awesome!

I saw it in person over at Matthew's house last month, and it came out
very nice -
much better than the picture looks in that earlier thread. Looking forward to your next attempt Matt! Are you going to go all out and have an underground Rancor pit and everything?