Huge plants don't necessarily mean more yield, just more to light up, I can only veg for as long as 34 days since they are always at a foot by then (from seed) by the end of their lives they settle between 2 and 3 feet tall, thats a lot to light evenly. Just don't wait too long to flower... As far as vacation, water the piss out of them (so water runs out the drain holes, you should be anyways) and go, trust the timers and trust they will not die, you will be fine, at worst they will be quite droopy when you get back.