Any tried and true methods y'all have used to help a tenant like this move out quickly and peacefully?

Each duplex will have 2 acres to itself, will be a very quite and peaceful place.

Peace to the forum.

I'm bullish on Metro Phoenix for the following reasons:1) population growth2) job growth - many companies are relocating entire operations here to capitalize on low cost of living, low taxes (corporate/personal/property), and friendly business environment.3) Low vacancy rates - rentals in 2-4 unit properties are in extremely high demand, often receiving multiple applications within days of listing.

Since it is an SFR and you are taking on roommates, don't underestimate a good roommate even if they aren't willing to pay as much as a terrible roommate, your peace of mind is worth a lot.

That will give you peace of mind while also hopefully giving you confidence that it is still a good deal even with the mold remediation. 

There is a real humanitarian side of being a landlord, a real ability to help people, to get them back on their feet or to give them a place to raise their kids in a safe and clean environment.

Its good to see this environment welcome's our skill set.

How can I invest smartly in real estate in this high price environment?

Assumable mortgages are a great benefit for a Borrower in a low rate environment, especially at a long term fixed rate.