It's dFR(or dfR) not DfR and yeah, APB is pretty cool.DfR can be solve intuitively and EOpair shouldn't be to hard. It's a really cool method. (And once you learn ZBLL you can use that too!)
I wouldn't recommend using Mehta as a secondary method personally because basically none of the stuff carries over to CFOP and yes, it has too many algs to be a secondary method imo.
I'd recommend ZZ or Nautilus(both 20-40 algs at the bare minimum)
That being said, choose the method which is the most fun for you because, in the end, the main goal of cubing is to just have fun.
My 2 cents.