Sorry for the lengthy delay in not replying to this thread much sooner but I've been buried in work and have just now come up for some air 🙂
I'd like to add my comments on the above suggestions.
Here's the catch – recording audio seperately adds time and complicaiton in post production. It WILL give you better audio, though.
In the absence of timecode (which I doubt you will be using), tools like PluralEyes makes this process a lot easier than it used to be.
Check out a Zoom recorder – it may do the job with XLR inputs and get good room sound.
No professional sound person will ever recommend a Zoom recorder. They're OK for very low budget/student work but not at the higher levels. A pro will have a multi-channel mixer recorder and be able to give you a mixed version of each scene along with the individual tracks. You may never need them but it's nice to know that they are available to you.
Minimum, get a solid wireless lav for one channel and a good boom mic/boom for the other channel.
A pro will have several different mics to choose from, depending on the location and requirements and, more importantly, know how to use them to get the best sound possible under the circumstances. For example, there may be times that only a wireless lav will work while other times a boom mic will do the job.
Make sure you slate properly, keep good records and practice good data management – especially with seperate audio.
EXCELLENT advice that everyone should be following!!!
If at all possible, try to get your sound person involved right from the start, especially if you're doing a location scout. Getting out on location only to discover that, from a sound standpoint, it's a nightmare will cost you money and time that you don't want to spend so listen to him/her as they know what they're doing. They will be able to offer you advice for issues that you have never even considered because they do this a lot and have the experience to help you.
Good luck with the project.
