For Firewire repairs both Brian at Inside Edge and Bart at the Beachbeat factory (not the UK one PRJ) are quite familiar with them and it's straight forward.
I've had Brian repair my carbon fibre/eps Van Straalens and my Diverse dynocore eps which has innegra cloth and repairs have been invisible.
If you get a ding with Firewires you need to get out of the water and the eps has to be dry before repairing it.
If it's just small fractures that can let in water you can sand them down and use Solarez : squeeze out of tube onto fracture and cover with clear tape to make it smooth, take out into good sunlight and peel off tape after a couple of mins, then sand flush if needed. Easy.
Fins wise with fcs I was running a similar sized fin template to the MR tfx in fronts and M5 rears today only because My stretches were in my 6'er which I'd left at home so these were my second choice.
If it was smaller I'd put GXQ's in the rears if I wanted to loosen up the tail.
My favourites are the Stretch PC cores. Set and forget.