Thanks for all the responses. Got to start somewhere so I will work with Peter's factor of (roughly) 2.5.
My largest kite (for TT) is 12 m. For an initial purchase, I am trying to decide between a 5 m or 6 m Echo. Leaning towards getting the 6 m (14 ~ 15 m kite equivalent) under the assumption that it would be the better choice initially for learning and I could keep it for subsequent use as an ultra light wind rig. I would likely have to purchase a smaller wing later on. But, fortunately, there is already a "6 and 4 m2 ?" thread that addresses which size to get.
If I went for the 5 m I might be able to get away with having just one wing.
One concern is that the 6 m wing would simply be too big. At a weight of just 56 kg it is easy to get overpowered. However, I am thinking that the instant (and what looks like total) de-power of the wing should provide some margin. Any other light weights out there who would care to comment on that ?
FWIW, my largest old school windsurfing sail is a fully cambered 6.5 m race but, if all goes according to plan, I would be using that in much less apparent wind than the wing + foil combination.
A used Gong 1350 foil just showed up in the mail a few minutes ago. No idea how well that is going to work but it was a lot cheaper than splashing out for a new foil. I am really stoked about getting into wing foiling especially the carving aspects. Kinda like the feeling of getting my first kite 12 years ago.