I will let Roger respond to most of your questions (I saw your comment on the school forum).
Regarding your first question on fins and top speeds, here is what I have found. I started using a GPS four years ago and had high hopes of reaching speeds well beyond what I have been able to achieve. Here are a few things that have kept me from going over 31 knots (my top speed).
Board size - I have an iSonic 111 (31.02 knots) and a Hifly Move 105 (30.30 knots). I feel that both boards are too large and wide for me to go much faster.
Body weight - I weigh 79 kg and feel that if I was heavier, I could carry a larger sail.
Water conditions - You need a long streatch of flat water (1/2-1K) with little wind disruption. Where I sail, at best I may get 10 seconds of good flat water before I hit a wind shadow or run into the shore line. Even though I have had two good opportunities to make speed runs in ideal conditions at another location, I still hit the wall at 30 knots with the same two boards.
Strong, steady wind - to break 30 knots on your board, you probably need at least 23-26 plus knots of wind.
Sails - I have Maui Sails TR race sails, so there is no handicap here. I think any top of the line race sail will be your best bet. Your sails are good, but may limit your top speed just a bit. You have to be on the edge of control to achieve your best and your sails will be slightly less controllable at the top end compared to full on race sails. My top speed was on the iS 111 and a Maui Sails TR4 6.6 in 25 knots of wind.
Fins - Something small without a lot of foil. The Drake fins that came with my iS 111 are good for speed, but tend to spin out often so I bought a Tectonics Tomcat. Probably not as fast as the Drakes, but no spin out and great control. Fins no doubt play a role in top speeds, but I think the other issues mentioned above are more critical.
Skill - I don't know how much my skill plays into all of the above, but I have been windsurfing for 26 years.
I am very impressed by the speeds achieved by so many sailors and wish that I could do better. GPS-speedsurfing.com list 500 sailors achieving 34.33 knots or faster, and that's the average of 5 ten second runs. The last guy listed (500) at 34.33 knots hit a top speed of 35.94 knots during one of his 5 runs. Take a sampling (click on the name) of several of the 500 top speeds runs and check out the details. This will give you an idea of what it takes to go fast.
Keep trying to go faster, hopefully you will find what works for you.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.