Regarding the sheeting angle for the primary winches, and that it affected by where on the toe rail the snatch block is located. Sorry that the attached picture quality leaves something to be desired, but it illustrates the solution on my Cherubini Hunter 36. A fixed position block is mounted on the toe rail at a spot that yields a good lead angle. The snatch block then can be moved fore/aft according to the jib size, whether is furled or not, and the wind condition. All without affecting the sheeting angle to the winch.
Pay good attention to the mounting instructions that will come with your new winches. Particularly that they need to be oriented according to the primary gear position. When I mounted my new winches (getting on 9 years ago), I noted the instruction. I mounted one correctly with the primary gear (say it was the starboard side winch -- can't remember now) oriented towards the toe rail. I then went in did the same on the other side. Just mirror it right? Oriented the primary gear side towards the toe rail. Later I realized that since the line always is wrapped around the drum from the right side, the port side winch primary gear needed to be oriented towards the cockpit. The mounting holes on my winches aren't spaced evenly around the base. So when I rotated the mis-mounted winch into the new position, I needed to drill holes in new locations. And fill the previous ones. Irritating error.
