Hi, welcome to Dreamviews!

You were definitely close; the ringing/buzzing sound is common when transitioning into sleep paralysis but from what you described (still being able to move your limbs) you weren't in full SP yet. Try relaxing and imagining sensations such as touch, smell, and sight, which will help you transition into SP and then the dream. Passively observe any hypagogic imagery or sounds, and don't focus too much on them.

As for your questions...

-Can some people just NOT be able to have a WILD? (even if you do everything correctly)
Some people find it more difficult to WILD, but I don't believe it's impossible for anyone. Some medications (such as antidepressants) may have an effect on how often one can get into sleep paralysis, though. Narcoleptics have a higher chance of getting sleep paralysis even if they don't purposefully induce it.

-I've got to a point I couldn't feel my legs or arms, but I feel I could still move them, is this normal?
I think that was just your body going numb; when I've been lying still for half an hour or so, I can't feel mine either. That isn't necessarily sleep paralysis, but might be the onset. It's best to just not move.

-Once you're in sleep paralysis, do you fall asleep, and you'll have a LD? Or do you stay awake the whole time?!
Once you're in sleep paralysis, you don't "fall asleep" in the traditional sense! Or, that's how I think of it. You're basically lying there in SP, your eyes closed, and then images and sensations start to form around you; you're basically pulled into a dream while your physical body simply falls asleep. It's a 100% conscious transition.