Being a full scale jetmech...please don't say fin...it's a vertical stabilizer and rudder or a horizontal stabilizer and elevator.....Sorry I am ok now....
Agreed get the gap as close as possible. When I use pinned hinges I cut out a little for the raised part of the hinge to set into....yes it does decrease the throw some but closes the gap and I have never come close to not having enough throw.
As far as the number of hinges I would probably do 3
Good Luck