The position of your lifting foil is what is important and the centre of lift of that being roughly in the same point as your combined centre of gravity of you and your board and components. If you install with 90mm parallel surf board fin rails you will have a little wiggle room fore and aft , but you can move your feet too of course so long as you are with in the scope of the board and the deck grip . i dont know where you intend to place your batteries or we could talk rough measurements. Typically you want your mast about 300mm from the rear of the board because your main lifting wing is further forward still and you want a foot stance of 500-600 mm apart , it is typical to place your rear foot directly above the mast, some pros are a tad further aft, and front foot 500-600 mm further forward, this is because the lift centre is aprox 200-300mm forward of the mast and your feet are balanced either side, plus the leverage of the rear foil putting a bit of extra weight on your front foot so you need to be biased slightly front footed and leaning forwards. i see everyone who learns with rear foot too far forward and leaning their body backward to compensate, this is plain wrong , also learners sensibly go too slow, however this makes it very hard to ride the foil , best ride is where the rear of the board is parallel to the water , not pointing upwards and stalling the wing against the thrust making it all unstable.