Back in the day when I raced sunfish as a kid I had a book called Sail it Flat by Larry Lewis. If it is still around you might find it helpful. Since this is a sailfish and wood that means that it must be at least 40 years old. I would check the fittings carefully especially the bridle where the mainsheet clips on at the back of the boat to make sure they are sound and replace as needed. I recall a nasty experience with having the bridle fail when it was blowing up whitecaps. Sailing performance such as pointing and weather helm can be affected by the attachment points for the halyard and the pivot for the lower spar. The tradeoff is in boom height (keep your head down when you jibe!) You can improve MA on the mainsheet by attaching a pulley to the bridle and running it back up to the lower spar. The sunfish has a little hook at the forward end of the cockpit which you hook the mainsheet under. Sheeting in single handed was accomplished by doubling the
line back on itself and grabbing the
line closer to the sail while releasing the end that you were holding. A bungee cord from a screw eye on the top of the daggerboard to the mast can help to hold the board up on downwind runs. Go out and practice self rescue a few times. These boats are fairly easy to capsize intentionally just go stand next to the mast grab a hold, lean hard and make sure you don't land on anything hard! Wear you pfd when you do this because it is a lot easier to get up on the board or the bottom if you turn turtle without one than it is with one.
These little boats are a blast, with the exception of windsurfing this is sailing at its most elemental. Hope you have a lot of fun.