Waist vs Seat can be a long debate but I find the waist more comfortable and versatile. As a learner you will find it easier to hook in and out of a waste harness.

Kite or Wind harnsses will work fine. A harness is like a good pair of shoes, needs to be comfortable and provide good support, and they're all a bit different. The best thing is to try a few on in a shop, they'll have a rope you can hook into so you can try it fully loaded with your weight. Good luck.

The kite harness has more of a hook on them, (or was it the other way around?) SHQ recommended that I change over the spreader bar when I converted to windsurfing. From memory I think it was about $40.

I use a kite harness it works well but it is time I got back to a windsurfing one! If it is your first one a waist harness is the way to go.