I don't know the answers to all those questions but can tell you the way I do it. If it looks like a plant is growing too stick-like and not bushy enough for my tastes I'll pinch out the middle right above the side-growth.

If a plant isn't showing any side growth often doing this will trigger it, but it could just kill the plant. Make sure you pinch off above a leaf node, since that's where the new growth will come from.

I also find that doing this between nitrogen-rich feedings helps keep things growing strong.