Carib sea is the only sand I've ever used. Some people will say it is not worth paying for it to get the beneficial bacteria as the sand will become populated with the same bacteria over time anyways, but simply just for the quality and grain size of the sand itself, I'd pay the extra for it
If you have sand already, then don't cover your current sand with anything more than 1/2" without waiting for a week or so for the bacteria in the bed to catch up. If right now you're bare bottom, I say add as much as you want. Just make sure to watch your water levels while you're doing so.
Also, I reccomend using a funnel with a peice of clear 1" hose on the bottom to add the sand and keep it from getting everywhere on your rocks.