Thanks for all the responses - I haven't been able to get back to the thread till now.
One reason for planning 16mm is to future-proof the project. I was at a MeetUp indie producer meeting in LA a few months ago, and unless I'm missing something, acquisition even for low budget projects seems to be ideally 4k. I'm not sure 16mm will scan that high, otherwise something as simple as the Blackmagic Pocket mentioned by Macks might conceivably work, notwithstanding artifacting.