It would be good to keep all dimples for accuracy. My AP only has 11 per sides as L and R are duplicates in their armour.
As far as where the wrist finishes on you arm, first you need to look at the gap between bicep piece and top of fore arm.
You need minimal gap at that end, and still be able to bend your arm. (Screen accurate has very small gap). The gap between your wrist and hand guard doesn't matter.
If your forearms are too long for you, trim the wrist end leaving all dimples, but entirely removing the return edge. I have an image in my build thread of the wrist ends with no return edge left, check it out.
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