I use 100 gal smart pots... next year I plan to use 200 gal... I believe if you have the space and energy get them big.

The only downside is the 100 gal pots use a lot of dirt...!!!

I don't tie back although I used too.... I recommend tying right before the flower because the stalk changes a lot in the flowering phase its better to not stress it out while it is flowering! I also don't recommend waiting until your plants are root bound too transplant... just before it is root bound is better, and don't transplant during the flowering stage... put them in the size pot you want BEFORE it flowers, this will give your plant the opportunity to put all its energy into flowering and not worrying about other things...