I have a 125 gal aquarium - it is 6' long x 18" deep x 24" high. It has housed a BRB, then a Dumerils boa, and now has a young Burmese python.
I use two large heat pads with it. The one on the cool side is at 82*F, the one on the warm side is 90*F.
I would strongly suggest having plexiglass tops made for it, and you can use the mirror fasteners to secure them. That will greatly help keep heat and humidity inside, and ensure no escapes.
Unfortunately there is a decent amount of heat loss through the glass so put a hide over each UTH. The air under the hide will stay warm, and you could make natural-looking Styrofoam hides which would insulate nicely.
I wouldn't load it up with water features. A few large bowls will suffice. Use cypress mulch as substrate, some driftwood for climbing, and some fake plants for décor.