First you need to cycle the tank. Going through the cycle first will vastly reduce the deaths of any fish. You will need a liquid test kit for ammonia, nitrite, and nitrate. No dry test strips because the chemicals on the strips start to degrade as soon as the package is opened and the strips exposed to the air. This causes faulty tests. Here is a site about the cycle. http://www.aquariumadvice.com/articl...q=2&fldAuto=21

Bettas can do well with several species. The problem is that most species like to nip fins, and the male betta's fins are exceptionally tantilizing. Possible tankmates include platies and swordtails, black skirt tetras, buenos aires tetras, diamond tetras, cories, kuhli loaches, and rasboras.

Most little fish are schooling fish. A well-stocked tank might be 3-4 livebearers or tetras + 3-4 cories or loaches + one betta. In such a small tank, stocking the fish all at once shouldn't throw off the cycle much once its established.