if you have the money then go large.
4 years ago i had a ludicrously over poweved inflatable. Keith you would have loved it! 40hp engine on 4 metre avon inflatable. I had 13 stone friends mono-skiing behind it. Then i moved on up to a 5 metre rib. What a difference! And now ive sold that and i'm looking at 6m ribs.
If you buy a small one after a year (or a few minutes depending on conditions) you will be wanting a bigger one.
As for experience, get out there and drive your boat in all sorts of conditions, its the only way to improve....