If I could have anything at all? Man, that IS a hard one...
300-odd gallonish corner tank (like the Tenecor Q-series
). Background slate. Built up terraces all along the sides and back of the tank. Visible substrate quicksilver sand (with planting substrate underneath). Approximately half full (paludarium). Canister filtration with the return positioned to create a waterfall feature in the tank.
Heavily planted with CO2 and ferts dosing. I would use anything and everything I could lay my hands on but on the wish list are Echinodorus 'Red Flame' 'Green Flame' 'Devils Eye' 'Crimson Sails', Anubias afzelli, Anubias barteri, Aponogeton madagascarensis, a few Cryptocorynes, rotala wallichii, parrot's feather, milfoil, giant val, some of the rarer mosses including Christmas moss. Terrestrial plants... philodendrons, ferns, maidenhairs, a couple of small epiphytes and whatever carnivorous plants I could lay my hands on.
Stocking:
Scleromystax barbatus
Corydoras loxozonus
Leporacanthicus triactus - Three Beacon Pleco L091
Pantodon buccholzi - African butterflyfish
An altum angel, maybe a pair
Dicrossus filamentosa - Checkerboard Cichlid, pair
Longfin rosy barbs - big school of those
Some rainbows... hard choice. Probably Melanotaenia lacustris, Melanotaenia boesemani, and Melanotaenia splendida splendida 'Atherton Ck.' That gives me a turquoise, a yellow/steel and a purple.
Shrimp. Maybe. I'd be kind of worried about them ending up as fish chow.
Terrestrial stock; equally hard choice. All of these are legal in Australia with a license (first 2 are natives.)
Litoria caerulea (Common Green Treefrog/Dumpy Treefrog/White's Treefrog)
Litoria infrafrenata (Whitelipped Treefrog/Giant Treefrog)
Agalychnis callidryas (Red eyed leaf frog)
Phyllomedusa sp. (Monkey frog. Probaby go for Phyllomedusa bicolor.)