@Jessica Lohr
I would double down on @Ryan Thomson's perspective going into your search.
Secondly, many people are unaware of the self sufficiency test for 3-4 unit MF. With rates where they are, I haven't personally seen anything on market that would pass this test for financing. In short, this test requires 75% of all the units to cover the debt service on the loan. A duplex, on the other hand, does not have this restriction.
Third, layering on an MTR or STR and your ne cash flow will be better, in exchange for additional work. Maybe your current workload would allow for this extra work, but perhaps not.
Lastly, I would challenge you, as I do with two of my clients going down the same path, to look at your calculations not based on cash flow but money saved. Since you mentioned you listen to the podcast, David Greene regularly talks about this. I believe it is critical in todays market.
If you current rent(s) in Cambridge for you and your partner are, for example, $3000/mo, and you purchase a duplex that generates $2500/mo LTR and your mortgage is $4000/mo. Your net cost of living has been reduced from $3000 to $1500. You're essentially "cash flowing" $1500/mo via savings, not to mention any tax benefits, amortization on the loan, and any appreciation be it forced or natural market.
I hope this help...
Now to actually answer your question of towns, how far are you willing to commute and what kind of financing are you qualified for?