As a Contractor myself, on my New Constructions I use Lawson windows and I NEVER had a problem with these windows that involves quality, I’ve had problems with the other manufacturers that were mentioned above.

Like you, I was concerned about potentially triggering a due-on-sale clause with the lender.However, I spoke with my lender, and while he confirmed that technically this could trigger a due-on-sale clause, he also mentioned that in practice, it’s very rare.

@Daniel Windingstad someone else mentioned Florida, I'll just chime in and say Florida is probably not much better for cash flow unless you go C/C- properties, but regulations probably are better than your current situation.

As mentioned above by others, cost segregation is an option.Additionally, contributing to your IRA is another option.

@Jagjit Singh Welcome to BPFirst you might mention what size multi family you are talking about.

If you paid cash for the 3rd property, absolutely put it in an LLC.If it has a big mortgage then no need as you mentioned above.

I have partnered with a number of production builders that are starting to do what you mentioned.  

As other suggested the places you mention above are a broad spectrum, so I would first take a look at / underwrite 10-15 properties in each area.

I notice you mention updated wiring and plumbing. 

Challenges have been mentioned above in the description Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?