One thing I have seen done with a lot of success is implementing a venture specific LLC for a deal involving multiple parties.

But this is what my clause about pest control says:(A) Pest control, after the first ten (10) days of the Term of this Lease, shall be the sole responsibility of the Tenant, including, without limitation, prevention and remediation.

Yes, the long term tenants are preventing me from updating the rental units.

Generally though, I break it down into the "five pillars" of protecting your assets.The first pillar is avoiding unnecessary and risky activities (don't drink and drive, insurance generally won’t cover your poor decisions) and take good care of your investments(maintain your property, etc) - these simple steps will help you prevent lawsuits before they even occur.

The other version treats it more like a note where official transfer doesn't take place until the note is paid, here she could evict you instead of foreclose, since you do not own the property yet you are legally treated more like tenant than an owner, but I think this prevents the due on sale clause since a sell hasn't fully taken place.

First I'm not sure if there's anything from a legality aspect that would prevent me from living in the 4th unit that's currently gutted and needing renovation.

Since the structure already exists, all you need to do is write it all out.These are some of the benefits I have found, and seen, from implementing Land Trusts with their LLCs.

I am looking to implement the BRRR strategy for long term buy and holds.  

Look this up on reputable websites, most notably the Centers for Disease Control and Prevention.

A few other positive things:If you have a home office it creates authenticity with the IRS and can diminish potential push-back you could get by claiming the deduction.Using an EIN helps prevent identity theft - stealing an EIN happens, but isn't as common.