I used to work with a marketing company who claimed they could get me leads of properties already listed STR. 

Quote from @Lolo Druff: I've heard horror stories about awful property management companies and am looking for a REFERRAL for a trusted source from an investor.

Fast forward, my brother and I co-founded a property management company in Boston, where we handle everything from tenants to transformations.

Currently, I own 26 doors and run a property management company that oversees 350+ units.

After all PITI, utility, and services (lawncare and cleaning) costs I have $7,225.I set aside 25% of this for my maintenance fund.The remainder funds my lifestyle, wife has a Tesla, and quarterly vacations as well as business growth.In 2023 I am tracking to build 4 duplex units designed as room rentals funded in part from a recent land sale.

But usually for a tenant occupied it's like $90-120 per monthI've noticed a lot of multi-family buildings are pre-WWII housing inventory - are there restrictions or issues common with that (historic districts, crazy high utility costs, etc)?

you can utilize a skip tracing company to get contact information for the owners.

Does anyone have any experience with doing a 1035 exchange between permanent insurance policies/companies?

Lots of investors utilize rentometer.com.

I hired an IRA-approved valuation company to value that note at that time.