couple of answers
1) Rake is different from prebend (hook). Rake is the angle that the mast makes when all of your shrouds are slackened. I don't know the precise measurement for the H31, but I'd take an idle guess and say that a weight tied to the main halyard should be around 6-12" aft of the mast at boom level. This is set by adjusting the forestay and backstay turnbuckles(after ensuring that the mast is straight athwartships). Prebend is then applied by adjusting the shroud tensions and the tension on the backstay. I don't know how much prebend is appropriate for an h31.2) The original mainsheet system is probably fine, but you might want to replace the line if it's original. There are 200 zillion ways to rig a mainsheet -- fine and gross tuning, double ends, purchases of 2:1 to 24:1, etc. A lot depends on where the traveler is located. If I were you, I'd simply sail it for a few months. If it's fine, it's fine. If not, then investigate.Vang, absolutely. Very important when running downwind.3) Not my area of expertise.