Best workflow to use with mixed footage from 7D, Nikon D7000 and Canon 550D

Hi,
We shot a band performing recently and id like to edit the footage together.
I wanted to know if it makes sense for me to transcode to DNxHD 36 for now, since my computer doesn't have very good tech specs (iMac, 2.66GHZ intel core 2 duo 4 GB Ram 800MHZ) and then while exporting the final edit, i could export at a higher quality like DNxHD 120? Does this make any sense?

What is the optimal quality that I should transcode to for the final export?

If it does make sense for me to edit at DNxHD 36 and then export higher could you explain the process of doing this?

Thank you very much