I agree that warm water is better for even guppies and you will have a much wider range of choices of fish. If you keep the tank at room temp. guppies will do okay but about the only other fish you will de able to find will be rosey reds, white clouds, and dojos, or local fish.
If you heat the tank a little (78F) you can get 3-5 pygmy corys, guppies, 3-5 lemon tetras or other small tetras, 3 danios, and even a dwarf flame gourami and a bamboo shrimp would complete the tank.
A small hang on type filter, 1 1/2" of fine grain gravel, a couple attractive stones, and a sagittaria and clump of java moss and elodea will soften the look of the tank. For a small tank I like the look of patterned blue tinted foil crinkled for texture and taped to the back of the tank as a background.
I disagree about the 6 weeks of cycling for a small tank.
Place in the rinsed gravel letting it slope slightly to the front. Add the rocks. Make sure you use dechlorinated water when you fill the tank and if you pour it in slowly onto a small plate that is then removed it will not disturb the gravel. Hook up the heater and plug it in then do the same with the filter, leave out the charcoal pack (just fill that space with a trimmed filter pad), then let the heater and filter run over night.
The next day check your temperature and if it is okay add the plants then wait one more day to let the tank stabilize. During this day you can, if the temp is near 78F, beg some filter sludge from your science teacher (a tablespoon or two) and add it to your filter. This will establish live bacteria in your filter. Then the following day add your first few fish, a few guppies would be best as they tend to be hardy, wait a couple days and add a couple more fish. then repeat the wait and add cyle until the stocking level is where you want it.
What the waiting and stocking in small increments does is give the bacteria in the filter time to catch up with the increased ammount of fish waste.
It would be nice to get a testing kit for ammonia and pH but for a tank like this it is not critical.
None of the fish mentioned are very expensive or hard to find and you will end up with an attractive tank.