About the NJP, I use the piano-ing method, and add a little trick so even if I input it too early, I still get a full combo:
So, piano-ing is basically holding up and slide you thumb over 2-1 after the dash. I know, this is well known from mk9 days, but there is an additional trick:
If you slide the thumb through 2-1 (and not 1-2), and always be sure to make mistakes on the side of anticipating it, sometimes you'll get the njp correctly and sometimes you will input it too early making the string 21 come out after the dash. Either case you get a combo, you just have to hit confirm properly to what happens. If you see njp hitting, follow up with 21, f412~ender. If you see that njp didn't come out, but the 21 came out instead, just do f412~ender. It's pretty much simple to react to.
This way, even when you fail, you succeed
Just make sure you don't press 2-1 too late. It's the only of the 3 scenarios you'll drop the combo.
And, of course, if you slide the thumb from 1-2 it doesn't work also. It has to be from 2-1 and inputing it on time or early.