20/4 and 24/0 both work great for autos in my experience. I actually have some afghan kush autos under 24 hour light. Anything below 20/4 will greatly reduce your yield with the autos.
They do veg but only for 2-3 weeks depending on the strain and then start to auto flower.
I wouldnt top an auto... or lst it or anything that will stress it. The life cycles of the autos are so short that you will see negative results in your yield from minor stresses. Even transplanting slows them down. Your best bet will be to plant them in their final containers from the start.
They dont grow very much during their veg stage but as soon as flowering kicks in they grow alot.
Hope I could help and goodluck! Dont forget to post pics.
DISCLAIMER: everything I post and say are lies. I am simply roleplaying. All photos were found on the internet and/or fake!! I do not grow or use anything illegal.