Anything specific to watch out for with lender approvals on a property this size?

Size of a flip will change things too.

Maybe an airfryer, apartment size fridge. 

Of course, your SPEC building background is going to be very important with a deal size this large and in the high-end luxury space. 

FoundationPlumbing, particular main sewer lineElectrical (on older houses) Main panel sizing, grounding, sufficient circuits for modern usageRoof (but you're good for 10 years, just get a tune-up)HVAC system (one again, get a yearly tune-up)

.+ Or combining STRs with medium-term rentals (travel nurses, corporate stays, etc.) to smooth occupancy and improve margins.It’s not a one-size-fits-all anymore, but with the right strategy, it’s still very doable.

Per code, as-of-right, a building with a CMX-1 zone designation is permitted a maximum of two or three dwelling units (dependent on lot size) plus any applicable housing density bonus pursuant to section 14-702(7).

And more generally — is there a max purchase price or loan size that DSCR programs will allow on 2–4 unit properties? 

For what it's worth, house hacks can come in a wide variety of shapes and sizes.

You can challenge the appraisal and submit your own comps (especially highlighting the lot size difference).Timing matters.