Ahead of you on both fronts! @
twocicle
#1 . FSA SLK tandem crank to double. Its a bit of a wish wash with FSA cranks... I have bought several of them now to figure out what does and doesn't work. the newer FSA designs (crank arms don't aesthetically match left to right this way) have the same rounded spline on the spindle while the ones that do aesthetically match use a square edged spline on the spindle. You have to make sure when you order the double crankset that the spline type matches- both 24mm and both the rounded spine profile.
#2 . Yes, Saint calipers work with R785 levers. Use the BH90 hose, its great. When you use the BH90 hose and BH90 olive/insert they work together. the flange to the lever is the same but the insert has different diameter to fit into the BH90 hoses. basically you could use either bh90 hose or bh59 hose but you need to make sure that you use the corresponding olive/inserts that match your hose. Being that im using the saint calipers, im also using the bh90-sbls hose that has the proper banjo bolt for these calipers! I have the final bit on order from my lbs for this bike but its confirmed to work.