If you're looking for a long term business associate, in my personal opinion it is best to team up with someone that you want to make rich.

Adjust what has been pertinent in multifamily and what has been pertinent in SFR to a better product.What is the difference between a value-add and opportunistic fund?

It is important that you control your funds and do not let he contractor get out ahead of you or you will be left with a overpriced unfinished rehab to salvage. 

Make sensible financial decisions by allocating funds for unforeseen fees, insurance, property taxes, upkeep, and mortgage payments.

I don’t own rentals in Portland either   We are new home builders and we supply funding for Rehabbers.

If I was in your shoes I would gently let that person know what you plan on doing with the place and how much you're going to be charging etc...

Personal preference though 

My question is would it be best to sell all 3 single family homes, place funds in a escrow account to 1031 exchange and then invest in a 10 or more multifamily property?

This answer all depends on personal preference and budget.

After a brief search, the IRS says-For tax years 2018 through 2025, if home equity loans or lines of credit secured by your main home or second home are used to buy, build, or substantially improve the residence, interest you pay on the borrowed funds is classified as home acquisition debt and may be deductible, subject to certain dollar limitations.