Cheers me brudda! We swap info-goods all the time, and you bud results are always in the top tier of all here that I've seen -
Hey Fitz'! .....hmmm, well that's one theory. I can tell you my mix was a tad hot, borderline even, but by no means enough to stunt them. Using a smaller first stage pot might be a better way to manage both nute load and size, but how big a pot need to be thought on more,...fabric of plastic too!
Fabric may be better for root management (air pruning action, forcing roots to grow laterally more filling the pot inwardly better, and having them feel the restriction from it?)... Plastic is worlds easier to transplant from though, avoiding root trauma and not having to hack a fabric pot off to avoid that!
It'll be tricky no matter what, the way they grew in this KIS amended soil was crazy, even in cool foggy conditions.
...thinking if one had a 10gal final pot, the middle stage pot should be around 5gal. I start in about 1/2gal pots with reg soil just to get them going, though a mild amended soil would be fine... Stage of growth-wise, keep them in 5's to restrict size some until mid-late veg', plant size depending mainly of course... with different cultivars, growth patterns, etc., this will be no small challenge!
In your case, topping is pretty much mandatory, 4-5th node, and some proper LST...
Let's see what
@KIS Tad has to say about all this,...