I think it's gonna be a much more subjective answer than any one person would like it to be.

Personally, I found it easier to step in the production role than it was to pick up an instrument. I'm learning Piano and Guitar now, but for the first two and a half years I was just doing synths and samples. I felt more comfortable with my computer, and everything just sort of flowed naturally. Learning a DAW was like learning a new video game, which helped a lot.

I feel like learning an instrument requires more physicality to master, and producing a track requires more intellectual investment to master - which isn't to say either one lacks the other or that either is inferior, just that the methods of acquisition are suited to everyone at differing levels of ease.

This contributed to hella drama on twitter. 

I say just start singing your melodies with your mouth while you're trying to make them. You probably know the way you want them to sound if you're just humming a series of intervals together - use that to your advantage! If you're still unsure, go pick 10 songs that you think have great melodies and see if you can recreate the melody in your DAW. Look at the direction of the notes, the length of the notes, and their rhythm. That will give you a lot of insight into the way they tend to work.

You have good instincts, though your inexperience shows - and that's not a bad thing! We all start out somewhere. How much have you referenced while working on this track? Have you done any analytical listening of other dubstep songs?

To be honest, this is why I don't like learning music theory from youtube tutorials and stuff like that. They give you a lot of rules that you're expected to follow without properly telling you why, and people develop an expectation that the rules are concrete and permanent and/or learn information that only makes sense when you learn fundamental concepts that get glossed over.

You can use any note and any chord in any scale, because almost every scale has the potential to play every single note, you just have to change the accidental. C Major contains every natural note (white keys on the piano), so the D chord you're referring to - D Natural Minor - would be called a diatonic chord - it only uses notes that are found within the scale. However, there's nothing saying that you can't use D major (D F# A) or D Diminished (D F Ab), for example, if you think it'll sound good.

I recommend everyone go to musictheory.net and spend a few days really going through the lessons one by one and trying to digest the information in sequence. If you can learn to read sheet music, comprehending theory gets so much easier.

Go find ten songs that have basslines you think are absolutely amazing, and write down everything that they do. Write down what the basslines sound like, what intervals are used, and what their rhythms are. Write down how they change between sections, and what sections they appear in.

This applies to the other threads you made (you didn't have to make a separate thread for each question, though  ), too. Arrangements, layers, etc. Don't steal from them, but use them as a guideline for your own songwriting.

Press F and click "All Files". That'll bring up the file browser so you can go hunting for your samples.