I dont really agree with that bowl pace first then let accuracy come later theory.
I played rep cricket at a pretty high level when I was younger, and I tried to copy McGrath. I basically hit a good line and length and didn't bowl express, yet I opened for my district.
Now I am older in seniors, I have about the same accuracy and I am bowling quicker than most guys my age. I think if you have a half decent action, speed will come naturally with age, but accuracy won't. You have to work on accuracy, but most of your speed comes from age, technique etc.