Mainsheet stack is 7:1. I will need to talk to you more about how to "site the leech". How do I know when the leech is at the max tension? I will have to mark the mainsheet with this setting once the boat is all back together & back on the water so I don't get the leech too tight.
I assume he is talking about rigging the boat on land, standing behind it and sighting up the leech. Pull the mainsheet in until the leech is in a straight line (perfectly in line with the mast).
Unfortunately, this setting has very little bearing on what your sheet tension actually needs to be on the water. Once you're on the water, the loads in the sail vary considerably with windspeed, and you have to adjust your mainsheet tension accordingly. For example, the max upwind mainsheet tension that you need in 5 knots is a LOT less than what you need in 20 knots. So that little mark you put on your mainsheet is likely going to give you bad information the majority of the time.
As the windspeed increases, the leech wants to fall off the centerline and so you need to crank in on the mainsheet if you want to go upwind. Pulling on more mainsheet tension (in conjunction with increased downhaul tension) also flattens the sail, so in higher wind, more mainsheet tension actually helps settle the boat down. Also, variations in the downhaul tension affect the required mainsheet tension. As the downhaul is made tighter, the mast bends and this causes the leech to fall off, again requiring the mainsheet to be brought in farther.
The best way to determine what your mainsheet tension should be is to install tell-tails on your sail, particularly in the upper panels. I recommend one set each in the second and third panels from the top. These will tell you very clearly if you are under or over sheeted.