I'm going with a 245G 72"x30"x27" and this run through I'll be running mostly sunnies. I went with the 30" depth for the gills-16" and so I could keep a bowfin later on. it's still too small of a tank for most bass though.
if you were planning on the smaller species like longears and pumpkinseeds -12" you could do quite well with a 125, although since it uses the same floorspace I would get a 180G.
if you wanted to go with darters and shiner types a 90 would work good.
if you wanted to do the smaller sunnies -dollar northern longears, or orange spotted, a 55 would work, but a 90 would be better.
if you'd like a pygmy sunfish setup, you could keep several pairs in a 20L or several dozen pairs in a 245G...
as with any setup, get the biggest you can. if you want to keep smaller fish, just keep more.
my bluegill came from my dad's pond, my warmouths from aquabid, my longears that I have, and the longears and green sunnies that I will order when available are from zimmerman's fish, my snails and plants came from ebay, and my texas cichlid came from a LFS.