1. Actually i found s of them are useful combos, except 15, that one's a waste of time and next to impossible to do right anyway. 13 is the combo you will be doing most of the time during curse, i think 10 and 11 are dive cancel stuff so that's good to learn. 14 is hard you should learn but there is a way to make it easier, for that i like to do 6a > 5d > airdash Ja > j4aa > 2a > 5b > 5d > airdash Ja > j4aa > 5a > 6b > j6d. Alternatively just ignore what i said and go to the combo thread.
2. As skye said, though i think this might not work on a few characters, maybe i'm wrong and i just mess up. In any case I always super jump after 5d in your scenario, you can do jaa> dj > ja > jc > jd.