You might want to consider setting up the tank the other way around. Set up your filter and everything, and cycle the tank using the fishless method. You can find instructions easily using google. After the cycle is completed, you can add all of the neon tetras at once since the bacterial colony will be large enough to handle all of the fishs' waste. Personally, I would put in pygmy cories instead of neon tetras because neons can rip betta fins to shreds. Cories will stay at the bottom and not attract as much negative attention from the betta.
If you put the betta in after the neons or cories or whatever you choose, he is less likely to be aggressive toward them because the tank is not yet established as his territory.