"I will go get some smaller pots, like 3 gallons.. go into 5 gallons right before flower"

That suggestion was made to me also but do you understand how hard that's going to be?! Think of a 3 gallon chunk of loose airy dirt with a big plant sticking out of it turning it upside down and then right side up and trying to put it in a 5 gallon container without it falling apart?! Sounds like a disaster waiting to happen. And especially if you have to do it by yourself. Even with someone else it'll be tough. Sorry. I'd go from the 6" containers right to the 5's. Not that much difference between the 3 and the 5 anyway. FWIW.