Agree with above.
My assumption from your post is that you might be learning in sub 10 knots as well? Learning to foil in light winds will be VERY difficult. If you have foiled (windsurf foil or kite foiled) before, you may stand a chance, but if this is your first foiling activity, you'll take ages (or may not be able to do it).
Skills. I'll assume you haven't foiled before? Ideally, get behind a boat and learn how to use a foil by being towed. Slow speed then gradually build up to the point of being able to lean back lightly to get the foil to fly. Then weight the front foot and touch down. Keep practicing until you can fly for long periods of time. Check youtube for tips on this. Wing skills - pump the thing up and go somewhere where there is a moderate wind and a softish surface (so if the wing gets out of control, you don't damage the wing if it hits the ground). Sand or grass are good. Learn how to hold it at the proper angle, pump, hold in neutral and gybe. Again, check youtube for tips on what you should be trying to do.
Once you have those skills, learning in 15 knots is the go. Excess power is easy to dump. The big area low aspect wings tend to provide a lot of lift but tend to be more draggy so can be a little limiting once you're advancing.
I learned on a 4m wing and it was too small. My biggest is 5.5m and that was ideal for me. Going much bigger, you need to consider how manageable the wing is, and how the tips of the wing will potentially touch down if you aren't tall enough to lift the wing. I'm 175cm and 70kg.
I learned on a 125L board and found it great. I'm athletic but don't pick stuff up easily (some would say unco

). Smaller vol will be more difficult. I'd be highly inclined to go biggish volume and small footprint. Others will probably disagree with me on this, but I've seen lots of learners go for too small a board (body weight +20 kg) and suffer. In light winds, if you can't get up and going, having the extra volume can be very helpful if you have to slog back home.
Ideally, try some boards before you buy so you know what you can float on with some degree of competence.