no problem, i had a tough time figuring this site out also at first.
it would be wise to let it keep running for about a month like you said, unless you used an old filter pad it is pretty unlikely that it is really cycled already.
you'll probably want to keep your tank a little warmer than 72 if that's what you're keeping it at. i think it might be better at like 76. that heater should be fine for your tank.
you'll want to get a few more corys, 3 or 4 more cory's. they are schooling fish actually. unfortunately i believe a height of 18" is recommended for angels. this is because once they get full grown their fins get pretty long, so for them to have room to swim around a bit this height is recommend. if you get the angels when they are small and if you are really going to get a 30-50 gallon tank (sometime within the next several months i would say) you could probably transfer the angels to this. although i have a 30 gallon and passed getting angels for it cause of it's height. so make sure to get a tall one. then again they might not survive that long with those danios. danios are very active fish, they might not be terrible fin nippers, but with the very slow moving angels it might be too much. i've also heard of people having perfectly peaceful danios, and also heard of vicious ones that terrorized all their fish to death, its probably just not worth it to try the angels in there. I would probably suggest a gourami of some sort instead, do some research on them. you can always get angels once you get a bigger tank.
yes a 10-20% waterchange is required every week. this is because of the fish waste being broken down from ammonia, to nitrite, to nitrate. nothing breaks down the nitrate so it continues to build up.
if you look into the species of dwarf/pygmy cories you could easily have 6 or 8 of them. there's some examples in this question i posted
http
/www.fishforums.net/index.php?showtopic=280608
i guess getting back to your original question (i'm sorry i didn't even realize this was the diy section, someone else might comment eventually), i believe i read once that you can use the polyester stuff used to fill pillows. i believe this might be the same thing you are talking about. the stuff i mentioned seeing at my petstore was not the expensive if you would be interested in that. hmm..i just did some searching, i didn't think of this but you could take your sponge and just cut it open and remove the carbon, just dump it into a trash can and try and get all the little bits out. then you'll have that plastic part still to keep your filter sponge in place. if you really want to you can cut this off, and by the polyester stuff and strap it onto the plastic frame with rubberbands...i haven't done this, and personally i'd be a little skeptical of keeping the rubberbands in the water, maybe a plastic twisty, or if you undo a paper clip and poke it through or something (unless paper clips rust?).
also you asked about washing the biowheel. washing your filter pad and biowheel should be done about once a month. when you do a waterchange and you have a bucket of old tank water just lightly rinse them in the old water in order to get any of the large debry off them.
check out the "new to the hobby" section. you will probably find some useful posts there about your regular tank maintenance.