I can't answer the first question, but I can answer this one:Originally Posted by Aspoiu Go to original post
Once you've unlocked the final manhunt missions, you simply go to the location in question (eg Roosevelt Island for Jupiter's mission), open the mission options screen (where you set difficulty and directives) and look for a 'toggle mission mode' option in the bottom left corner of the screen. Use that to switch between the normal and manhunt versions of the mission. (If the same mission is part of the weekly invasion, that's also an another version it will toggle through.)
Manhunt missions are: Roosevelt Island (Jupiter), Tidal Basin (Hornet), Coney Island Amusement Park (Shaeffer) and Camp White Oak (Lau).