The buoyancy of the mast is plenty. As soon as the mast hits the water, the boat swings round so the mast is upwind. if the mast was removed, the boat would right from the windage on the hull, beams and tramp.
The boom has 80 kgs/176lbs buoyancy (200 was a good guess), which should be enough, especially as any waves and the wind are both working to right the boat.
You are right about pulling the boom beneath the water. There is a strut required. It is attached to the mast at deck level and the lazy sheet runs through the end. The strut sinks to ~45 dgrees and the sheet can be tightened, pulling the boom under the water.
A lee float was not considered for the following reasons:
1) weight in the wrong place
2) complexity
3) they may stop a sideways capsize, but that is much less likely than a pitchpole. In a pitchpole, the bow goes in and then the boat capsizes to leeward. Almost certainly, the first part of the float to get wet will be the top. Then, it will make it impossible to right the boat without outside assistance.
If the sheet fuse is used, capsizing will not happen. I certainly do not wish to encourage people to capsize, just because the boat can be easily righted.
Foils are complex and prone to damage when they hit things. This is not what Bucket List is about. If you want a foiler, then it would be better to start from scratch, as the boat would be very different.
regards,
rob