I'm starting work on my first documentary (30 minutes) which I hope to sell for broadcast.

I'm used to editing for broadcast news, and the channel I freelance for has a rulebook for audio element positioning:

Channel 1: track and English translations of SOTs ONLY (left channel only)
Channel 2: all original language SOTs (English or otherwise), PTC/standup, natsound – i.e. everything else. (right channel only)

I send them split track, the editors there adjust and do the final mix.

However, as I'll be delivering the doc complete (hopefully) I might need a different set up.

Any advice?

Every broadcast doc we have delivered has been "wide mono": dialog mono on both tracks and stereo music panned. Of course, talk to your broadcaster first. If you don't have one up front, mix as needed at output.

Cheers Shawn.