Depend on whether you are into freestyle or waves or both.
Purely freestsyle then depanding on butdget, you can have the following options.
Big kite 13m or 11m, small kite 9m or 7m.
13m 9m is the combo for me and I am 86kg but then I also have a 6RPM for the really windy days as the bridle system on it is really good. Flies like a fuel stearring wise but has more of a wind range. Reality is that you won't be unhooking much on your 6m anyway.
The other way you can extend the range of your 9m is to have a set of lines which are 20m instead of the standard length. This does 2 things to your 9m, it reduces the initial power generation as the kite has less window to travel through. It flies (Appears to) fly faster, but that is because the kite is so much closer to you.
Shorter lines extend the wind range of your kite but you still get benefit of bigger kite for freestyle and not having to increase your quiver.
For waves 11m fuel so you can freestyle and then 8m RPM as they are really good freestyle kites but great cross over for waves.
Purely waves new octane or last year Rev 2.
My two cents about slingshot option as the post was about fuels. There are other brands out there, but Fuel is the premium freestyle kite and with the newer ones you can get away with two. Everyone at my beach does.