210gal... I'd mix community and semi aggressive. I believe that species like tiger barbs and the bigger gouramis could get along with tetras, livebearers et al if there were enough space.
75 gallon - Nice big shoals of tetras, clown loaches, gouramis, angels, huge group of cories, shrimps, 5 swordtails, 5 mollies, 5 platies. Have a planted natural tank (if I knew how to make plants survive)
125 gallon tank. 60" long x 24" deep x 20" tall. That would be the perfect size for where I want and as big as I would like to maintain. It would start out as a big freshwater community tank. And maybe after 5-10 years, I would relaunch it as a saltwater setup and use the 55 gallon that I have as a sump underneath.
bigger wide and tall something like 12x3x3 sand substrate river bed style decor ie big roots huge bogwood rocks etc stocked with south american cichlids sevs geos etc . heaven!!!!!!!!!