Re: old sails?
Battens in the pockets - yes - and with the thin end forward.
About that leech line - it can take out a lot of flutter and realistically the reduction in airfoil qualities from the curl it might put in the leech is probably not going to matter much. But be SURE you don't have the leech line tight and then start hauling in on the mainsheet. You don't want several turns of mainsheet pulling against that tiny leech line. Loosen leech line, tighten mainsheet, tighten leech line.
A sailmaker can tell you a lot from the sail even if it's not on the boat. Walk in with it under your arm and chat. Preferably at a slow time if you can tell whan that is so they can put it on the floor.