Re the Boards.
The majority of opinion is that sticking to a TT while you get yourself fully dialled with you kiting is the easiest road to follow. I tend to agree. If its a temporary thing then try to find any old TT thats way over size - eg a big old 150. Anything big will do the job & you wont lose anything in the changeover (big TTs hold their value).
BUT - others will say theres nothing wrong with going straight to a surfboard. IMO this would only hold true for those who are already accomplished short board paddle-in surfers.
TT's make it simpler & quicker - generally speaking.
When starting on your surfboard - first up or as a transition from TT - get yourself a biggish short board - say 6' +/-. Go strapless in flat water for a few hours or a few sessions till you get the difference from being propelled along by a wave to being pulled along by a kite - theres a big difference. Practice your turns, toeside & heelside etc etc till it all feels comfortable.
The hit the waves. Try it strapless at least once - you might find you never need straps. No loss if you want to go back to being strapped - for a while or forever.

Re the kite. Cant advise unless we know your weight. Generally one full size up from recommended 'just right' size for weight & conditions is a good move. Makes learning easier - slower kite - steadier winds. Then it leaves the way open to get a smaller kite once your big kite is TOO big on the day. Then go a full size down from that 'just right' size.
Hey Presto - you have the perfect quiver.

Good luck & remember - no-ones ever right or wrong as far as kiting goes. Different horses for different courses is definitely correct. Add in 'for different jockeys as well!!

Forgot to mention,inskip at DI for flatwater during winter, and brand pending a 11m

On a surfboard (and in the surf) people often go down a kite size compared to a twintip. So if a 12 is your normal kite (twin tip) then you could consider getting a 9 or 10 for a surfboard. Ideally you could have both.

Possibly start with a 12 and a twintip. You need to get advice from locals - if the wind is often 25+ then a smaller kite would be the go.

Here is some indicative kite sizing info: kitesurfing-handbook.peterskiteboarding.com/progression/choosing-the-right-kite-size

east coast winds and surfboard = a 10m kite.

my 10 is my biggest kite, if you need bigger its not worth going out.
be sure to add smaller kites as well once you get hooked.
i have 6,8,10.

I'm fairly sure that the Rebel can't be converted to 4 lines.

If you want something that can be converted back and forth, get the Fuse.