Do a quick search on Dipping Powders above and you should find plenty of information as it does crop up quite a lot in here
In the meantime, I did the training course for Cuccio's Powder Dip. I would ask your insurance company if it's a requirement to do the training, but I would always recommend training for a new system anyway and this is a very different technique.
To be perfectly honest with you, I rarely use it now! It was a novelty in the beginning but it didn't suit everyone. I now use other products that I'm getting better results from.
You can use it under gel polish, but as before, I think there are better overlay options. It isn't easy to build an apex with so you tend to get very flat nails with it. A lot of people have had trouble gel getting their top coats to stay on. You can't use normal gel polish top coat. You can either use a non gel polish top coat (can't see the point in this to be honest as it won't last), or you can use a hard gel top coat. I haven't had any problems using Salon Services UV top coat though.