BAD420,
I've used rapid start with good results. I generally don't give my girls anything for the first 2 weeks. Just water. At 14 days I start, but it all depends on how they're looking.
When I do use it, I start at 1ml per gallon when watering.
I generally stop using after the third feeding with nutes.
And as far as LST, Go for it.
It's easier than most folks think. I use wire coat hangers cut to length and I bend the end and stick into a side hole on the airpot.
Just make sure not to bend any branches too far.
Your just guiding it in the right direction.
Keep doing what you doing, everything is looking great.