When learning your going to want to use a kite that has a little more power than less power - it makes it somewhat easier as it's hard to learn if you feel like your strugling for power and it takes the fun out of it. Take a look at all the kites that are available to you and read up them on-line.
If your a windsurfer and you like your seat harness - stick with a seat. There are advantages to a waist harness but personal comfort is the defining factor (I use both)
Boards the bigger the board the easier to learn on, having said that too big a board and it's basically useless once you've progressed. I in all honesty (and someone will disagree) I don't think that going over 140-142 is of any use and I wouldn't go smaller than 135 (to learn on). If you can find a good board to spend the season on and get another board next year go bigger and use it for as a light wind board next season, if not go a smaller board. Underground, north, naish, cardboard, nobile are all fine boards look for a board that gets classed as "free ride" they tend to be more forgiving than boards designed for new school or wake style riding.
If you go a smaller kite (10m) I'd go the bigger board if you go the bigger kite (12m) I'd go the smaller board



(which one did you want?) enjoy the water