I would personally keep the 302 and trust its pre-amp to power your mics over the camera. Most cameras have fairly noisy pre-amps in relation to dedicated audio gear, so keep the Sony at line level and run phantom from your 302.
When I have shot doc footage before, I didn't have a field mixer and always wanted a better way to mix multiple mics when interviewing multiple subjects, as the mono L/R of the camera make for more work in post.
The camera itself will work fine as a recorder. You don't so much need 24-bit/96k on voice overs, and your production sound will already be synced. And if you're like most doc filmmakers, you're shooting 100+ hrs of footage. Syncing sound isn't always the most fun thing...