1) John is correct - Regarding tactical vs. strategic movement: Units can either move tactically OR strategic movement to redeploy - not both in a movement phase. Only tactical movements is allowed during the mechanized movement phase.
2) The convoy zone has a maximum amount of damage that an be inflicted upon it - not maximum per individual sub. Example: A North Atlantic convoy zone is worth 10PP + potentially up to 5 more Lend Lease PP. Therefore, a maximum of 15PP worth of damage can be inflicted (if the US is maxing their lend lease in this sea zone) to the convoy zone by one or more subs and surface raiders.
3) There is no limit to the number of AA guns in a territory - but each attacking plane can only be shot at once per round, regardless of the number of AA guns.
4) Each lend lease territory or sea zone has a lend lease PP limit. For example, the US can lend lease up to 15 PP to the K via the North Atlantic (5PP for each North Atlantic Convoy zone).
Hope this helps