Yes, finding a used GO board (of any size) in good condition is kinda hard anywhere.
They are very popular and sailors keep them practically forever as there light wind "go to"
If you are sailing with the centerboard up, then you really don't need it so go for the GO 175.
You are a big guy, so lots of width, lots of liters and a big 9.0+ sail are what you will need to
progress unless you have winds that are over 15 knots all the time. Not too many places in the
USA have these conditions.
The 5.0 m2 (if you have a very light mast) should be pretty good for your 16 year old daughter.
Something smaller and lighter might be better but if she is fairly big and strong, and you teach her
the correct way to uphaul and get underway she should have no problems with the 5.0 m2.
Have her use the centerboard at first, until she no longer needs it to stay upwind.
Hope this helps,