This doesn't really answer your last question exactly, but I never used to bother working out precise rates of descent, as it never unfolds exactly as you expect.
A good baseline rate for a 2:1 profile was 2500fpm (based on a descent speed of 230-240 KIAS). I'd tweak it up a little with a tailwind, down for a headwind, and just monitor the profile all the way down.
It's worth mentioning that the profile I mentioned before is rather generic, and I'd use it in anticipation of a visual approach - if I was joining an ILS or other instrument approach, I'd adjust the profile to ensure a smooth and stable transition, as you don't want to be coming out of a 2:1 at glideslope intercept.