Since the contributions have to come from the business income (PM biz) it’s not likely you’ll come close to taking advantage of the high contribution limits of a Solo 401k.

You can determine if the cost segregation study makes sense by speaking with your accountant and many cost segregation professionals offer a free analysis.

They can offer valuable insights into the local market, potential rental yields, and specific considerations for a rehab project like the one you're planning.

Offer aid and housing options if you're able -- don't try to profit. 

If you want to quote out high efficiency boilers for six Tripple deckers for example requiring installation of separate gas, meters etc. etc. - that might be a situation where you would want to work with a contractor directly because you would have lots of different options with widely varying costs.

I recently read in Forbes that investing near growing transit hubs can offer great appreciation potential.

Couple other things to consider, property / school taxes are high, and tenants have lots of rights.

It’s true that many property management companies are now incorporating tenant benefit packages as part of their offerings.

I won't just write them all here but I highly recommend contacting a qualified 1031 intermediary to walk you through the process.

If you’re offering $450K, then you could offer to take over the $120K payments and seller finance the remaining $330K.