[Edit: Hi, this is my first posting...sorry it's so long...and started writing it before you posted your final fish wish list...so never mind about some of the following. But there's some good advice anyway, IMHO.]
Where to start? Lots of potential problems with your selections. First, the leporinus gets waaaay too large for your tank and will likely become rather aggressive in such a small tank. The plecostomus, assuming it is a "common" pleco will also get too big.
A clown plecostomus, however, would be OK, as would some other species (bristlenose, etc.). Dojos do better in cold water. Mollies like it warmer (and salty). Platies would be a much better choice for you. Many loaches don't do well with salt. Peacock eels like to hide under the substrate and coarse gravel may injure its skin (and lead to infections). Tiger barbs are rather scrappy/nippy and do best in larger schools (they can chase each other around instead of your other fish). I've had "good" tiger barbs (ie peaceful) and really nasty ones that will pursue other fish relentlessly.
OK, some better news: Some types of small cichlids would be OK. I'd recommend kribensis, keyhole cichlids or curviceps for a beginner's community tank. Rams are also good cichlids for a community tank, but much of what you'll find in your LFS is from inferior stock and won't live very long. Of the other commonly available smallish cichlids, jewel cichlids can be extremely aggressive and firemouths less so (but still risky).
Gouramis: Dwarf gouramis would be excellent although more than 50% of the ones I see in stores are sick (with weird infections that can wipe out an entire tank). They are also horribly inbred in many cases. If you're not confident about identifying a healthy fish, don't get dwarf gouramis. Pearl gouramis are also good community tank inhabitants, although they can get fairly large. Gold/turquoise/platinum gouramis might get a bit too big for your needs. Honey gouramis are small and peaceful and the males get very beautiful once they've settled into their home (they usually look very dull in the store).
There are lots of tetras which would be ideal: lemon tetras, bleeding hearts, black phantoms, rosy tetras, head-and-tail lights, red minors, diamond tetras, etc. Black skirts get big and fade to gray, Buenos Aires tetras get big and can be a bit aggressive, "glass tetras" or "red eye tetras" (Moenkhausia sp.) also get a bit large. Neons and cardinals are great if you can get good ones. Get 6 or 7 of one type instead of 1 or 2 of several. A personal favorite are Congo tetras; they get a little large, but are fine with anything they can't swallow and the adults are very beautful (the small ones at the store will look like plain, silvery fish).
A few other suggestions: smaller rasbora species would be perfect, as would some of the smaller barbs such as cherry barbs and checkerboard barbs. Dwarf neon Australian rainbows would also be excellent--they often look bland in store tanks but become very beautiful at home.
I hope the fish at your Petsmart are better than the stores near where I live. Ironically, the chain-type stores are generally terrible places for beginners to buy fish because neither they nor the employees know how to properly ID a healthy fish. Don't you have a "real" fish store near you?
