Would not do neons, that's a lot of fish for a very little tank, and neons are very active and like swimming space, so they'd get stressed in a 5 gallon. Generally, the minimum footprint recommended for them to be healthy in is a 20 gallon long tank. In a 5 gallon, almost all of your options are just single fish, such as a betta or a pea puffer.

Something not included with the tank that you'll need for pretty much any fish you want is a heater and a thermometer. This is one of the cheapest heaters I've found, that is still adjustable and works well.