You do not need a 2 bolt base, that's for sure.
2 bolt bases are normally used for wave sailing in BIG waves where the board and
rig get "tumbled" alot.
If you are only sailing in small waves, or in flat cohppy water there is no reason to use a
2 bolt base.
You can simply screw a single bolt (on center if you can find one) mast base into the
I'm not sure that mast position is nearly so important on an SUP unless you are somehow
racing it against other sail powered SUP's.
On a slalom board..... yes, it's important... wave boards also, as well as freeride boards.
Most longboards have an adjustable track and it makes a big difference in longboard races.
I would suggest you NOT cut out the EVA deck until you have sailed the SUP quite a bit
and made your own determination that the provided inserts are not in the right places for
the way you sail your SUP.