No mileage restriction or requirement, and no minimum number of stopovers.
But, when you go to compare the SQ fares to, say, *A or xONEx fares, keep in mind that you will need to buy tickets from YYZ to the west coast, and then back from JFK to YYZ. If you do those legs in paid First, it may add a couple of thousand dollars to the total (in the US, we can close the gap SFO or LAX-JFK for $700 on VX, or the gap to IAH for $650 on CO; but the last AC biz class ticket I bought SFO-YYZ was $2225 each way....).
Still: RTW in First for US$7700 to $7800 all in beats *A by almost $4000.....and you don't have to stay gone 10 days.