I agree with much of what Joe W has suggested.
Big boys need very large beginner toys.
If you are young and athletic and live in a place with about
15 knots of wind most of the time, and GO 170 and a 6.5 m2 rig might
be a good place to start, but if you have less wind, or give up on things
easily, I think a full sized Start or Rio (LARGE) would be a better place to
start and increase your chances of success.
And, as Joe suggests, going to a windsurfing center and getting some lessons,
on their equipment, could give you a much better feel for what you are getting
yourself into here at a significantly lower cost.
If you like it, you can use the schools equipment until you have mastered the basics
amd then try some different boards until you find out what suits your size and your local conditions.
The GO could be OK, but it does not have a centerfin or center board so staying upwind while learning the basics could be more difficult.
Hope this helps,