Don't go to SD and then to MPEG, or if you do, go to 4:2:2/uncompressed first. I'd recommend that you render your mpeg straight from the HD timeline.
In terms of framerate which is what your question implies, it depends on what you're after. 24p will save disc space and give you a film cadence, which you may or may not like.
Outputting as progressive either way, is likely the best long-term option.
I understand you need to render straight from HD to the mpeg2 file that goes on the DVD. From my tests so far, all the different formats look as good as if they were shot that way. From what I'm seeing, I'd say 24p rendered from 60i HDV looks a little sharper than 24p stretch mode anamorphic from a DVX100A.
30p is looking pretty good to me. Will widescreen 30p DVD's play back as true 30p from a progressive mode DVD/TV setup?