I don't know how you sleep at night, literally! Don't the filter/airators make to much noise?

Or are u just a heavy sleeper!!!
If I were you I'd go with the largest aquarium you can afford/fit in your room. As for the piranas, it's probably a good idea to sell them before they get too eggressive, i hear you can get quite alot of money for the piranas. After you do that you could think about getting some other species of fish, or set up a community aquarium.
It's frustrating when all the water condions are perfect and you have some fish die/disapear! I heard that Demseys don't eat their babys and i'm not sure that convicts do or not so mybe the convicts ate all the babys (remember i dont no much about convicts!!). Another possibility is that the baby got sucked up through the filter. (Another terrible thing to have happen to you!! :P)
I hope some of this helped you at all!!

AngelSta