Sailplan
I just did a check on sailplan measurements, I'll put them here and let somebody else address your other questions:SAILPLAN MEASURMENTS I is the distance from the point where the top most jib halyard (and usually the headstay) meets the mast, to the deck at the sheerline (not the top of the house). J is the distance from the point where the headstay meets the deck to the forward face of the mast, at deck level. P is the length of the mainsail luff, from the head of the sail to the gooseneck fitting (or, on same racing boats, between black bands). E is the length of the mainsail foot, from the clew of the sail to the gooseneck fitting (or, on some racing boats, between black bands). LP is the distance from the clew of the headsail to the stay it’s set on, when the line between them is perpendicular to the stay. Note how the LP will vary when the clew of the sail is moved up or down.