Are there advantages in board size for water starting? For example, if the board doesn't sink too much, maybe that is a good thing? Or maybe not?
smaller board is easier because its possible to sink the board under your body weight, and then you can use the buoyancy to help lift you up. Whereas a large board sits on the surface and you need the sail to do all the lifting. Also the bigger board is sitting on the surface so there is physically further to travel. And a bigger board is generally much wider and its a little bit harder to get your weight over the centre line..
Also a smaller board is much easier to maneuver, and there is less risk of kicking the fin.
If you can find footage of a wave sailor doing a no wind waterstart, it will show all my points!
edit* round about a 130-90L for an 80kg sailor is about right.. but were spitting hairs here, technique is more important!
Agree with Barn - too big is hard due to the width and bouyancy. Obviously too small can be an issue too. How much do you weight and what board / wind strengths / sail size K Dog?
It doesn't matter what board size you have. It comes down to techinque, sail size and wind strength.
If the breeze is too light you can't waterstart
If the breeze is too strong welcome to catapault city (for beginners)
Depending on your weight and sail size, look for around 15 knots with a suitable sail that has the grunt to pull you up.
Big boards are harder to get your foot onto, but easier to get going once your up and vice versa.
There's a heap on the net and books (Peter Hart has a great one) about learning to waterstart.
Use what ever size board you can comfortably sail and gybe in the conditions, otherwise you're going to be practicing your waterstarting a lot!
Smaller boards are easier to waterstart, but may not suit your capabilities or light winds.
yeah but width makes it harder.
I still agree with Barns 130L estimate, that is plenty of float but not too much.
Yes I would say a 135 would be a little easier to waterstart than a 155 but not a great deal.. Don't use the board as an excuse, even if you stick with the 155 just keep practicing and attempt the proper technique and it will be a cakewalk..
If you can waterstart a 155, a 135 will be no different
90 vs 70 would be a difference, but you have so much positive bouyancy in a 135 it will be fine.
Buy more gear 
