Hi Mick,
You'll be surprised how fast your up and going, for the first few weeks it feels like it's never going to happen. Then you wonder what was so hard about it, and you sound like your determined so you'll be fine.
About the board, well yes the advice you have been given is good. Depending on your size and weight, if your around the 75-85kg then 130-135 might do 85-95kg then go for something around the 135-140. I'm 95kgs and ride a 138 and 140 but alot different widths and ones a mutant for waves.
By buying a board under 140 it will take a little longer to learn to stand up, but you will continue to progress better once up and riding. You would want to sell a bigger board shortly after standing up and riding up wind.
BTW learning on any unstrapped board like a surfboard will be difficult. You would be much better off buying a TT board, or hire a begineers board from a shop for 2 weeks to learn on then go get a board.
Anyhow hope that helps and good luck