Search the forum before you set your mind on doubling up in the hammock- general consensus is it doesn't work. Not sure what suspension you'd need to accommodate any "extra curricular activities". Other than needing another tree (or 2) a second hammock shouldn't be a problem to pack on a bike
Punch some numbers in here to see the forces your suspension is under laying still.
60yds of Amsteel is WAY more than you'll need for 1 hammock. Once the DIY bug reallybites ya' a 600' spool is BARELY enough