paint polystyrene black and stick it behind the tank... insulates too, lol...
i am spending too much time and money on my fish. its ridiculous. sometimes i wonder what happens to my student budget, lol... I will look out for small lights - not sure that i have seen any that will be good for a nano....
u can hide a sponge filter in the corner or the bottom of the tank - cover it with a copious amount of plants.
I don't think i will be that concerned about filtration. ill do partial waterchanges once in a while.. as the mood sets in, lol.. there will only be 1 fish in there, occasionally ill put a female fighter in there, to keep him company.