I only did some preliminary testing with moving the fins, but it seems like the board get a bit looser with them forwards and more tracky with them further back. I just normally put them in the middle since I have not experienced anything I like to change. Might start to play with it more when I'm more tuned into the board.
Mast track. I run it right in the middle in all conditions and with all sails. I sometimes move the boom up and down 1 cm or so depending on conditions. And in fact, I prefer it a little bit higher in choppy windy stuff. I think this gives me more control of how I load up the board, so I can take load off the front which gives me a smoother ride. I never have problems with the nose "flying" anyway. But all this is very, very individual.