RE: First Shortboard
Since you have a Start board available, and you have a 7.5 m2 Retro, I'd suggest using that combination ( a little larger Retro would really be better if you have < 12 knots of wind often) to develop your basic shorboard "skills".
Tart with the foot straps in about the middle position (front to back) and try to get them all the way back and outboard as soon as you get comfortable with them a little more forward and inboard.
The idea here is to continually keep learning, but challenging yourself.
If you continue to reconfigure the board at a rate that gives you a little
challenge all the time.
A mid to large sized Carve (161; 145; or 133) would be alot easier to learn on than the older narrower F@ as they are significantly wider.
The GO 139 would be OK as well, but it's a bit on the small side for someone your size. Perhaps look for an older GO 150-170.
These boards would make your learning curve much easier and expedite getting your skills to advance.
Lessons could help, but why Aruba?
Try somewhere with slightly more beginner friendly conditions.
I'd suggest Bonaire.
No worries with offshore winds, getting blown out to sea and being rescued, etc.
Books and videos can be good, but they just give you alot of things to try once you get out on the water.
TOW is the real answer, and TOW with lessons can advance your skills really quickly.
Hope this helps,