A common strategy here would be to move out of the townhome -> rent the townhome out -> house-hack and live in a new property with low down payment.

Can someone please tell me if there is a list of common house hacking start up costs and expenses I should expect?   

For example, I'm assuming that I don't need to notify the tenant before we come in to the common areas for maintenance.2) As far as I can see, the previous landlord was not paying the tenants simple interest on their security deposit when they checked out.

The common legal reasons to not renew the tenant are to move in family or to do a rehab large enough that tenant cannot live in the unit.  

My issue is that in the opinion of the remediation contractor (who has a financial incentive to recommend as much remediation as possible) all that wouldn't reduce mold levels long term, due to the fact that it's a basement in Portland, and the levels on the report are extremely common in basements in the area where no water intrusion had happened.

I've just noticed that finding 3-4 unit properties in Houston is not common.

You could look at going into title as tenants in common where you each own an undivided interest in the real estate.  

It is also common in commercial loans. 

There are several threads here on BP with servicer recommendations, but here are a few of the common names in the industry.

Tenant doesn't move anyone else in.90 day inspection ( watch for cleanliness).Pot smoking is very common.