Yes, different species can school together, but only in larger aquariums. You have to provide 3-4 of each species you want the school to mix together. So in your case, I suggest choosing one species.

The maximum of schooling fish varies with tank. For a 10 gallon, 6-8. You don't want to make it really cramped. As the tank sizes get bigger, the more space there is. Then the little tetras or barbs have a feeling a predator is around and to block that feeling out, add more schoolers. So the minimum rises up.

Heres a setup that sounds nice:

6 of any schooling species

1 honey gourami

OR

3 cherry barbs

1 honey gourami

1 platy

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If life gives you lemons, squeeze them into people's eyes and run away!

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In short, you're looking at no more than twenty inches worth of fish provided that they are all around 2 inches in length. Using this length approximation doesn't work for larger fish or larger tanks, but it is okay for your conditions (if it's easier to remember). Just remember to add no more than 3 fish at a time.

As to whether or no shoal will combine depends greately on the species. In order for it to work in your case, the species would have to be very similar and in the same family of fish. For eaxample, glow-lite tetras and head-and-tail light tetras, since they are so similar, will school. On the other hand, cherry barbs and neon tetras wouldn't school because they look different and have different behaviors. In short, if the fish you choose are in the same family (both are tetras or both are barbs) and they look very close, then you could only get three of each and put them together to form a school. As this is hard to do for a small tank, I'd only go with one species.

Hopefully I didn't confuse you.

MOA

"Tears aren't a sign of weakness, they're a sign of poor plumbing."

--Dead Men's Lies

Now, I know I need the heater and thermometer, but how long should I have that in the tank before I buy the fish? Also, is there anything else I would need to do to prepare my tank before beginning to purchase the fish? I just want this to go well. I don't want any problems. I haven't done anything to the tank since the comet died. I got him out right away, but I haven't changed water or filter or added any thing except food to keep the cycle going.

1. Buy heater and thermometer and set up in aquarium. Adjust thermostat gradually (no more tha a 1/6 turn per 20 minutes) until the tank temperature reaches 78 degrees Fahrenheit. (FYI, it's best to place your heater and thermometer on opposites end of the tank so that you get a more accurate reading.) Once this temperature is maintained for at least three hours, then the temperature part is all settled.
2. Make any adjustments in baking soda additions that need to be made.
3. Check water parameters (you know the drill, pH, hardness, ammonia, nitrite, and nitrate). If ammonia and nitrite are at 0 ppm, then you're good to go. Otherwise, do a 25-50% water change and post your ammonia and nitrite numbers so we can see what's going on.
4. If all the above checks out, then you're ready for fish. (Remember to acclimate them properly.)

MOA

"Tears aren't a sign of weakness, they're a sign of poor plumbing."

--Dead Men's Lies

The above link is a thread that contains some information on acclimating fish, if you need it. Have Fun.

MOA

"Tears aren't a sign of weakness, they're a sign of poor plumbing."

--Dead Men's Lies

Since I'm gonna be able to get the crushed coral, what do I need to do with it?