Big question, lets narrow it down.

No point in kiting on a trad wakeboard, too heavy, but there are kiteboards that will do both.
Dont start with boots
Dont start on a surfboard
Dont start on something with heaps of rocker because it is too hard to get upwind at the beginning
Dont start with something really expensive cause you'll probably change your mind about what you want and how you want to ride.

In your position, I'd start on a second hand bigger board that will do you for a light wind board in the longer term. 138 freeride style works for me at similar weight. It will be easier to learn on and do most things just fine. You can then demo lots of other styles of tt or directionals.

My 2 cents

You asked for n00b advice so here it is When I was researching my third board I found this out; you pick a boards length based on your height, i.e. if you are a 7ft bohemouth you want a longer board to accommodate the leveraging action of a taller person so that the board doesn't porpoise all the time; you pick the board width based on the wind speed and kite size you intend to go out in. Width determines how quickly you will get the board planning. Most newbies really need to get a board/kite combo right for approximately 20 knots of breeze, as that is your optimum learning speed.

As an 80kg dude I assume you're probably going to start with a 10m kite and a board around 138/40-42. Given you're a surfer you'll probably want to jump into the waves early on so something with a bit of rocker to help in the froth and chop. I started out on a North Gonzales which matches all those attributes, it gets going really easily and you can carve on the waves. You get a bit of elephant foot trying to keep an edge but you cant have everything. Boards are one thing you should really buy second hand to start with, kite shops and seabreeze are full of broken dreams that are in mint condition and half of what you pay new. Once you figure out your style you will want a different board for sure.

Have fun!

Get an FLX that is a few years old (around 2010 or so) - cheap, awesome, and go well for noobs and advanced guys.

Im 100kg and ride a 135, its plenty big enough for me

Hi ToshAuer
You have asked several questions there that I think I may be able to answer. Firstly, yes you can ride wake boards behind a kite, but they have too much rocker and too much of a curve to make them enjoyable. It is a constant fight to stay upwind with them and it is a bit like sailing towing a bucket behind you. This is exactly what you want behind a boat cos it stops the line going slack as you go out the edge of the wake, but not good behind a kite. Spend a bit of money on the rite board, or it will hold you back.
There is nothing wrong with going for a wakestyle kiteboard to learn on, but wait till you have mastered the basics, of going upwind small jumps, and recovering your board.
I just got a pair of LF Influence 126's for my kids, they have been kiting less than a year and really took to it well. The influence is not too much of a full on wakestyle board and does not have too much rocker, so makes a good first wakestyle board. The width is more important than the length and you are a similar weight to myself, and I use a board 42cm wide.
The One's are perfect bindings to use, and with a wakeboarding background, if you can get something like the 137 influence, (or FLX), you will take to it like a duck to water.

Hey Tosh, you're in Qld, which probably means you are going to be in the waves most of the time and realistically your average kiteable wind is going to be about 13 -14 kts. which is why i use my 15m kite 5 times more than the rest of my quiver put together. But the most important piece of I have is my LW board. up to 17 kts I don't even bother with my 140's 136's 135's. I like to boost and carve and you need speed to do that in the waves. You lose traction and planing in the white water, waves and with negative value water flow (which the is a lot of in the surf - 9 times out of 10 the water flows same way as the wind).
I hate the 'walk of shame' and so many times in this sub 18kt range my mates are on big kites but small TT s and i am the only one staying upwind and boosting, often on a smaller kite than theirs. A big TT is your best bit of kit.
As a beginner you'll be doing nothing on a 10m and a 138 until it hits 18 kts. BTW you'll be a noob for more than 15 seshuns
If you're serious about getting as much planing time as possible (ie learning to fly the kite while you're up on the board, and then boosting the crap out of it) you'll buy the biggest boat you can get to maximize your chances. Katz is right - forget about SBs for now but he is prolly on flat water in Vic so he doesn't have water current issues that we have in the surf.
King George, Spike, Glide, are the names to google and 145 x 44 is the minimum size you want. Mate if people call them boats or laugh just think that your 5'10'' x 18 1/2" shortie is actually 177 x 47 and that turns pretty easy. and also remind them of that call when your out and they're on the sand waiting for gusts or contemplating a board with wheels.
Turning TTs is mainly in the fins (40 - 50mm max cutaways are the best) and the style of the board is important but a blanket rule for now is avoid reverse outlines. Some asymetricals are good but some are pigs so for now just avoid them too.
Rocker is important and I like the flat ones in the big boards but I'm getting a King George soon which is highly rockered compared to my last LW but the high rockered boards are a lot more fun and easier to sink an edge so there are points for and against. With design there are a lot of relatives, of which you have mentioned basically all of so, the only way to be sure you'll get going is to go 145/44 + and work back from there. Be aware of boards with kicked tips as they are great for chop and hooning around but the true measure of the planing ability is reduced to the measure where the board flattens out. Also soft rails reduce your ability to cut and 'edge' so they also reduce your effective size.
You should be able to find one of these big TT's somewhere for under 500 but if not it wont matter as it will be your best and most used bit of kit.