Speaking purely from the standpoint of you qualifying for another mortgage, you at least need to charge enough to reduce your debt burden and get your DTI ratio below say 50%. 

Then ask what it's worth for them.There's no time for them to accrue any meaningful amount in that time span if charging purely interest. 

For context, it's a $700-800k 2-unit MF, which I'm indifferent about in terms of going the owner-occupied vs pure investment route.

This post is purely opinion based although I suppose some may have experience with this.

Neither party really has the ability to fully control the agenda so both are going to need to accept some significant compromise positions, and where that will fall is at this point just a pure guessing game.

Two ways to look at a house hack:  from a purely investment perspective, or from a housing cost reduction perspective.From a purely investment perspective analyze a deal as if you as one of the unit tenants will "virtually pay" yourself the same rent as the other tenants. 

Tellus is purely mobile and the UI can be better, but so far it's been good enough and their tech support is very responsive.

Windows and smoke detectors will be our first go to purely for safety concerns.

So if I invest outside of NYC it will be a pure rental investment. 

Our primary residence is purely just our residence with no investment or rental portion.