Technically both A and B are correct. A non precision approach does not care what glide path you are using, as long as you fly the correct lateral path and stay above all minimum altitudes.
However, optoon A is more complicated, error-prone and may lead to several problems, like unstable approach by being too high.
Option B is ok, but still a bit difficult, as you need to hit the FAF at the right altitude in a continuous descent. Passing FAF above platform altitude is ok, but can lead to the same problems as in option A. Passing FAF BELOW platform altitude is a no-no!
Option C would be to descend to platform altitude before reaching FAF and start final approach at the FAF. That’s by far the simplest way and avoids the pitfalls of options A and B.
As for the ATC clearance. Once you are cleared for approach AND established on a published segment of the approach (eg. on final course, before FAF). You may descend as you like, to the minimum published altitudes for the given sector. There’s no need to obtain further clearance for lower altitude from the ATC. Approach clearance is all you need...
@ Safelife - CDFA means Continuous Descent FINAL Approach (my bold), so it only applies after passing the FAF. It’s a common misconception that you have to start it earlier and can lead to several problems, like eg. getting it wrong and passing the FAF below published altitude.