Determining your final pot size depends on how big you want each plant. For indoor plants I like to transplant as much as possible. If you start out with too big of a pot, the plants small root system can't get to the corners, and as a result, moisture may sit and stagnate, causing root rot. The unused soil spots will also become depleted of nutrition.
The best way to avoid this is to let the plant become root bound and constantly increase pot size little by little. Refreshing the soil AROUND the root ball, so that fresh roots can access fresh soil.
I find it best to start a seedling in a red solo cup. It will become root bound in a few weeks. Move up to a 1-3 gallon pot. Then I like to finish(flower) in a 5 gallon. Ive never used bigger than that for indoor grows. If I did, the plants would be extremely difficult to contain.

Hope this helps, best of luck to you.

:greenthumb::jointsmile: