Well, there's no exact science. You should just start slow and work your way up, monitoring your water parameters throughout. There are experienced fish keepers who keep tanks that some people are shocked to hear about- but you really can't judge the tank without knowing the filtration and water change regimen. There is are clearly overstocked tanks, but many are just full and could be judged either way.
Nothing about stocking 1 betta, 1 snail and a shoal of cories in a 10 gallon tank makes me uncomfortable, and it seems that other experienced fish keepers on this site agree. I think this is perfectly reasonable for your tank and long as you give it the proper maintenance, and wouldn't really try to calculate the 'exact bioload' and there is no such way to calculate that.