I'm not a Color expert, so I can't comment on the best way, but here are some ways.
You could use built-in R3D support. You'd have to read up on it, because I'm not familiar with it.
You could use Red Rushes to convert your R3D files to image sequences that Color supports: probably DPX or 16-bit TIFF.
You could use Red Rushes to convert to ProRes 4444, with basically no loss of latitude in theory. (ProRes 4444 is 12-bit, just like R3D.)
You could use Red Rushes to convert to ProRes 422, giving up some latitude when you go from 12-bit to 10-bit.
Any one of those can scale your footage.
If you want to take an offline cut ? an EDL or XML ? and use it to conform your high-resolution media in Color, and you probably do, then there are various workflows for that. Crimson Workflow is one tool for doing that; Monkey Extract is another. You'd have to do some reading up on both of those and on Red offline-online workflow in general.
The better question, though, is why you'd use 2K as an intermediate step if you're doing an HD finish? If you're only finishing in HD, just drop everything down to HD and finish in HD. Less complexity. (This doesn't apply, of course, if you want a 2K master for later film-out.)