I weigh 80 kg and have a Starboard F160. I mostly free sail the board but I do race a few times a year. I think you will find that anything from the F147, 159, 160, 161 to the new 162 will work really well for you. I had a 147 before the 160 and a friend has a 159. I have used everything from 11.0 down to a 6.5 on the 147 and 160. I got down to the 6.5 in two different regattas with strong winds (25 to 30 knots). I go with what I am comfortable with while the "serious" guys were on 8.5 to 9.5 sails.
I think you will find that one small fin will work well for higher winds. I actually use my Deb. R13 70 M down to my 8.5 sail and then I go to a Curtis 68 for higher winds. Of course I am not beam reaching in the stronger winds and I haven't found the fins to be too big. I don't think you need to go much smaller than a 65 or 60 at the absolute smallest. A good custom fin will give you a much broader range than the stock fins. The Drake fins that come with the Starboard Formual boards are ok for light winds, but are a handful when the wind picks up. You might find a good used Deb. R13 65 somewhere for not too much $. In the lighter winds 8-12 knots, a 65 fin will hurt your early planing a bit, so having two fins will be a big help.
My favorite sail is my Maui Sails TR 4 9.2. If white caps are just forming (10knots), I can get going pretty easly with the 9.2. I do use my 11.0, but the comfort range for me is 8 knots to about 15 knots. The 9.2 works fine up to 18 to 20 knots.
It's all about practice and skill, plus dedication. Most serious formula racers can hold very large sails in strong winds. My example is not the norm, but I work hard at getting the most out of the smaller sails. The only place I really get hurt with the smaller sails is running deep down wind while racing. If you aren't racing, there is no reason to hang on to the big sails in strong winds. However, if you think you will get serious about racing, then you have to commit learning how to handle the bigger sails.
I think you will love the formula boards for free sailing. I get a kick out of chasing down cats and keel boats and blowing by at 1.5 to 3 times their speed.