Two Things:
First, How big of atank do I need to grow out platy fry to become large enough to sell. 5 gallon, 10?
Second, how big of a tank do I need for five tiger barbs, 3 gold barbs, 2 platys and a snail?
10g should be adequate for the platy fry. It depends as to how you want to sell them. As feeders? As pet fish, you'd have to keep them for 8 to 12 weeks before sale.