The 355 days varies by airline. As others have said you are besrt to try as close to that as possible but it will depend on the date of your final flight unless you want to keep making changes at $90 a pop.

SQ is virtually impossible to get F rewards on across the Pacific as they now use A380 or 77W aircraft on all routes (other than EWR) and block partner F rewards on those aircraft. OZ is a good choice if you can get it and as others have said NH is difficult but good. UA is probably worth it if you can't get F on other airlines but should be a last resort.

As for the AC sectors, as long as they are within North America, the fuel surcharges shouldn't cost more than $50 to $80 which would be cheaper than the positioning flights.