cool bro, looks good.imp:

you should be able to transplant at any time, if you are careful, and have good solid roots.
I transplanted, 2 4ft plants from 1 gallon to, 3 gallon. in the middle of the flowering cycle, came out great!. (Yea that's correct, 4ft tall in .89 gallon pots with CFL's )
You might want to separate those 4, if you are planning to let them get tall. you will need some sort of cage if you keep them all together.