Depends on your final finish type. I only use enamel on wood boats, and one or two part for FG. I pretty much stick by manufacturer guidelines for reducing, thinners etc.?
On FG I generally use a 1 part PU just because it's more forgiving to roll and tip than 2 part LPU yet gives good durability. Not awl grip but..the finish quality is totally a result of excellent surface prep and application technique...a guy here just did an amazing 1 part job with a bristle brush....I am confident about petit and interlux but have a preference for epifanes. Their multi marine primer makes a great tie coat between systems. On alum spars, I use a 2 part primer, 3 coats and top with one part PU.
