fly is the 2nd best chest workout next to bench. works nothin but pecks (which, is your chest) on chest day, i do my fly's on the cable machine like bent over doin the terrell owens wing flap. on chest day you should do bench, fly, and incline dumbbell, probably 5 sets of 5 reps b/c you are bulking.
you mean a decline fly? well anywho for chest keep a flat, incline and decline exercises of free weights will be best for all around development. for the single arm/leg stuff, if you can do 10 on one arm and only 7 on the other, your dominant arm will continue to grow stronger and the weaker one will stay weaker. obviously if you did your weaker one first and got 7 and then just do 7 with your stronger one there is no problem. Well just a note for beginers.
cables are good, but dumbbelps help you work all your stabilizer muscles, which is a must for looking ripped. plus it works your chest hella also. so do dumbbell incline press along with flies and bench press.