thanks for the replies and advice everyone!
yeah, i know that corydoras do well in larger numbers, to be honest, the reason why i'm so aprehensive to get more fish in general is that i love my fishies now and i don't want to maybe bring a disease into thier home!

i can't change the temperature unfortunately, its preset. but the little panda seems to be perfectly fine with it.
the pebbles don't seem to be a problem either. i've kept a close eye on thier barbels and they haven't got scratched up or missing or anything so far, so i think they're doing alright with the gravel.
i had first bought 3 pandas but 2 died. so the one little guy was alone for a while, and when i brought the two new guys home (plus 5 glowlight tetras) he would not leave thier sides for and an instant! it was very cute!
(tetra story: i had 5 glowlight tetras and everyone worked very well in this community and were very happy together. i would change thier water 25% once every week and everything would be just fine. then, one night when i was doing the partial water change, after i put the new treated water in, the tetras and 2 of the shrimp were acting very funny, like they were in pain or something!

i was really worried! the corys were acting a little sluggish too. so after that, everyone was ok, but all the tetras died within 1 hour! i still cannot figure out what caused this! i don't think it was the water temperature of the new water either, as they've never had a problem with it before. any ideas as to what caused this?)
i don't know what all my levels are specifically, i don't have a home water testing kit, but a month or two ago, i brought a water sample in to get tested, and the guy there said that for such a young tank (abt 3 months old) the water was quite literally perfect! (that made me happy too ;) hehe)
i was thinking about maybe getting 2 or 3 albino corydoras to add to the tank. what do you think? though i really would like a fishy that sticks to the glass of the walls..
thanks again everyone! (sorry this was so long winded again!)