Hi knifefishfreack,
3 gallon is a nice size ... most adults can live long lives in a 3 gallon. 5 and 10 gallons are a little easier to heat and filter, (more room).
5 bio-gold is too much IMO... 3 per day, tops. I would suggest a smaller food, like betta bits.. bio-gold expands a LOT in water, imagine how it affects their stomacs.
If and when you get a 10 gallon, just avoid the temptation of adding a lot of fish in there with him. Bettas dont like company, period.