Atsar,

You have an excellent grow going there!!!

As for the humidity do you have ventalation fan to remove the heat? if so you can take that off the timer and have it run 24/0, that's how I have mine running. You need to maintain some kind of air exchange from outside the cabinet to get the moiture out at all times or on a humidistat. (not cheap)
As for hight restriction I would remove the shelf or you are going to need to tie them down, mine are 5 weeks into flower and stopped going up in the last week from what I see they will strech another 6'' to 10'', I put mine into flower when 12'' tall now they are close to 30'' tall.