Hey friend, so from my experience the bigger the pot the bigger the plant can get (more root space very important), i did a couple 1 gallon smart pot and they were always small. I think a 5 gallon smart pot is more than enough for an autoflower plant. I just put a mephisto from it's solo cup into a 5 gallon and it's the biggest happy one. Wait for the roots to be pretty strong in the cup before transplanting and watch for overwatering in the 5gal for the 1st couple weeks.✌️ happy growing