potting

Would it b ok to start a seed in a 3 gallon pot to avoid a transfer?

Yes

Absolutely. Being able to use one larger container for an entire grow would make your plant much happier. Eliminates the stress of a transfer, and the plant never becomes stressed by running out of room for roots. I would recommend paying careful attention to how much you are watering early on though, because the roots wont be using the whole pot yet, so over or underwatering is a concern early. Depending on how large your plant gets, 3 gallons also is probably smaller than ideal, I would recommend going to at least a 5 gal pot if you are trying to do a 1 pot grow, but i dont know what size lights and whatnot you are using.