This write up is excellent and very helpful. Thanks Kevin.First, I would recommend a stopper knot in the tail of the halyard at the clove hitch on the gaff, or top boom. The spar will rotate under load and pull out. That's not a fun thing to have happen while on the water.
Now for a little technical info that may be helpful, I'm assuming you are new to sailing, so if you are not, I apologize in advance. I find that with a little knowledge, what happens on the water is much easier to explain. If you want to have fun sailing, then you want to be comfortable and in control. To be in control you have to understand the forces of a sail boat so that you know what your actions are doing. When in control, you will relax and thus be comfortable and have fun.
Basically, there are two parts to any sail boat, the sail plan and the hull. Both are creating lift forces in 3 dimensions as they react to the wind and water moving around them. All the forces of the sails centralize into a center of effort as do the forces of the hull. The boat is in balance when the centers of sail and hull line up and you can control any imbalance. On a sunfish, the sail's center is moved in relation to the hull by the halyard, outhaul, cunningham, vang and the mainsheet. The hull's center is mostly a factor of it's shape and location of it's foils, daggerboard and rudder. You goal is balancing the forces so they hit equilibrium, sailing is fastest when things are balanced. Steering with the rudder creates drag. Luffing the sail spills air and creates drag. Drag slows you down. Drag is no fun and we want fun.
The sunfish is particularly easy to demonstrate the effect of moving the sail in relation to the hull to achieve balance. For instance, you are going for a casual sail in light winds, you tie the halyard fairly low so you don't have to duck the boom and head out. You have a great time. Why? Because it's fairly easy to control differences between the two centers of effort. You hike out in small gusts or ease the mainsheet. The next day the wind is blowing 15 knots and you don't change anything before you head out. You have a rough time, out of control frequently, lots of time spent righting the boat and scratching your head about what happened. Why? Because the forces are higher as the wind increases, therefore the differences in centers of effort of the sail and hull are harder to control. When the differences are beyond your control things go wrong.
So how do you fix the situation and have a great sail in higher winds? You move the sail's center of effort in relationship to the hull's center of effort until you find a balance that you can control. This is highly personal because weight, fitness and conditions factor in. Step one, stop the boat from heeling so much by lowering the sail on the mast. The lower sail lowers the center of effort so you can control the heel of the boat by hiking. The boat will be flatter, and that's good because the hull will naturally go straighter when flat in the water. Now you notice that you are pulling on the tiller extension like crazy to keep the boat on course, this is called weather helm because you are pulling the rudder to weather (into the wind) to keep the boat from heading up into the wind. The explanation is in the center of effort of the sail and hull. When the center of effort of the sail is aft of the hull's center, the boat will spin into the wind. To change this you adjust the gooseneck back on the boom which physically moves the sail forward taking it's center of effort with it. Bingo, the weather helm is reduced and you are in control. Fun starts. Life is good. This is why you go out sailing.
The other controls I mentioned help further tweak the sail's center of effort. Vang holds the lower boom down which is important when you ease the mainsheet. Without vang the boom rises which increase draft (curve of the sail) which increase lift which is not why you eased the mainsheet. The vang works to keep the draft of the sail the same allowing the mainsheet to effect angle of attack, but not the draft of the sail. This is especially handy when reaching. A vang can be tied with the tail of the halyard and is worth figuring out. The outhaul tightens the foot of the sail which makes it flatter. Flatter means less draft which means less lift which is easier to control. The cunningham tightens the luff of the sail which pulls the center of effort forward. Note that a cunningham is less effective than moving the gooseneck so it's more of a fine tune control. Using vang, outhaul and cunningham is usually referred to as de-powering the sail. Racers spend years to figure out the best settings.
To get started, all it takes is a few wraps of tape around the gaff at different positions and a wrench to move the gooseneck if you don't have a quick release. Add a little knowledge. Then experiment until you feel comfortable. Add controls as you learn more and want to change things while on the water. Halyard tied on 106" from the tack is generally a good starting point with the gooseneck in the low teens forward of the first sail grommet.