Yes... 7/14 means 7 windsurf sail and 14 kite. Second question is impossible to answer. Highly dependent on how the conditions actually shake out, rider weight, board size, and most importantly, kite flying skills. Meaning... more experienced guys, as ive witnessed, are very good at "flying" the kite on the very bottom range, sheeting, looping, etc.
You mentioned a few times you are "new" to the sport. Aside from lessons, how much on the water training have you had (in hours)? Have you learned upwind riding in both directions proficiently? Can you transition turn? Have you relaunched in deep water? Body drag/ self board rescued? Since you haven't told us any of this its really hard to guide you as we all want to help you. But if you have not done (and Im just assuming here) a lot of self training on the above items with at least 10-15 sessions and 30+ hours, I would HIGHLY caution you on just showing up at Deer Creek on a 5/10 day with shifty g to 20 kts. Toss in some lulls too.
You want my beginner advice (as I a one also) head to Rush while its still deep enough. Great training spot, flat water... and SHALLOW. That's the best way you will progress. Craigs forecasts have been pretty accurate and I also use windalert to follow wind station readings and forecasts.
If you are already at 40+ hours and have done all the basic stuff then my bad. Im just looking out for you as I got myself caught downwind when self training the first week after my lessons and it was a LONG hitchkike back to my car
Something I'll never do again.