training a level canopy is only important for indoor growing.
outside it's high PPFD from all angles. just spread it out with training any which way you want.
also, it's already flowering and in a po. it has much more limited growth than a typical outdoor plant. it probably won't get big. Do figure out why it flowered -- did you cause it or is it the light/dark cycle outside (specifically length of uninterrupted dark being 10h/day). If not, it will re-vege and that'll be a mess to deal with in the meantime until your sunrise/sunset puts it back into bloom phase.
fertilization.. is it fully rooted? if yes you treat it like any other plant. It's no different at that point, relatively speaking. If still early in process, just try to ramp up slowly, but if you see any deficiencies add more sooner.
i'd wager 2-3 more weeks of vege growth before it fully abates. pot size looks fine relative to that guesstimate. shouldn't inhibit vege growth potential, given early flower context (assumes it is not a revege).
revege -- you'll see weird leaves (quickly escalating in number) and odd stem elongation. Leaves with smooth edges or only 1-2-3 lobes etc. don't confuse with single-bladed sugar leaves for false positive.