RE: fin for 147?
No expert racer here... But as your question has been left unanswered for a few days, I thought I would share my experiences.
For light wind days I like my Deboichet R13 70 S+ +6, but when the wind sets in I switch to the R12 70 M+ (and a smaller sail). It is fast, but the angle is reduced.
I have been playing a little with the newer R17. In short I have found that the R17 M is a little dead feeling, whereas the R17 S is too powerful for the F147 board (and our weight). So my expectation is that the less powerful R16 S or S+ could work well.