first off, as far as plants go. Josh's and a few others have excellent selections. i can point you in the right direction if you want to expand your plant inventory. as far as home depot and lowes plants goes, they use a grower names Angel Exotics. they grow really nice quality plants, but beware, some of them will outgrow a viv rather quickly. so research the plants before you buy. fittonia, pilea, peperomia and dracena are all good, easy to care for plants that should stay a decent size. another option is to find a garden center that sells terrarium plants. mini terrariums are all the new rage in suburban america these days and more and more garden centers are starting to cater to that part of the hobby. if you are still stuck, let me know what you are looking for and i can ship you some, just cover my expenses.
as far as heaters are concerned, i am a big fan of aquarium heaters under a false bottom, but that is probably because i am an old aquarium guy and it's all about consistency in that hobby. if you have uth's laying around, by all means, use them. just remember to place the heater on a DRY side of the enclosure. a side where there is no water feature. and keep it about 2" above the false bottom. i'm not a big fan of those ceramic heat emitters due to the humidity that rises from the tank. moisture, heat and electricity bad!!LOL

now, as far as your background, a few options. remove it and build your own, remove it, cut it down to the false bottom height and re-silicone it, or just build the false bottom to mate up with it and it can have a sort of "dug in" look. be creative, go nuts!!