Assuming the deck where the cleats mount has been repaired so that it is strong, regular flat SS washers should be ok, but if you want to go better, use fender washers, which are larger in diameter. If you are not satisfied with those (I would be), then you can always make up a metal SS backing plate, drill holes in it and place them under the deck.
Your jib sheets can take 5/16" in diameter, or if you want a little larger ones for easier handling, then 3/8" tops. I like Samson line and so then you would pick the trophy type, which has a fuzzier finnish for grabbing, rather than the XLS halyard type, which have a shinier finish (but they will work too). The length varies with the size of jib. The larger the jib, the longer the sheet. You can measure it. Figure if the jib is sheeted all the way in on one side, you need a sheet to go from that corner, around the front of your mast to the opposite side and through the blocks to the winch (around it a few wraps) and then to the cleat plus enough tail in excess. Obviously the larger headsail will require a longer sheet. If you are going to buy one sheet for all sails (obviously a pair - port and starboard), then get enough length so that you accommodate the largest. Otherwise, have the right sheet for each headsail.
