Hey Achieve, it really sounds to me like you're over complicating things for yourself. Top now, top tomorrow...either way will be fine. I'd recommend reading Uncle Ben's thread in this section,
https://www.rollitup.org/advanced-marijuana-cultivation/151706-uncle-bens-topping-technique-get.html there is a lot of good info, and I can tell you from experience that it works. To put it in a nutshell, you grow the plant to 5-6 nodes, but then you top it above the second true node to get 4 main colas...
The other thing you mentioned, not watering during lights on...as long as you're not splashing water on the leaves, I don't know any reason why you can't water during lights on. I can't imagine indoor would be different from outdoor in that regard.
Back to the first thing I mentioned, over complicating things. I understand that this is your first grow and you want to do everything right and end up with some smoke when all is said and done...I understand because I'm doing my first grow this year also, I'm growing outdoors, and I went through a period of time where I was making the entire process a lot harder than it had to be. I guess all I'm trying to say is that you're going to end up causing yourself unnecessary stress and anxiety by worrying over every little thing, you'd be much better off in the long run following one simple piece of advice: KISS, Keep It Simple Stoner.
Good luck man.