This part is important, and you must ask this pointed question (in writing, preferably) to someone at the financial institution with sufficient understanding of the banking industry. 

Since we buy value-add properties, the vast majority of my time is spent managing (and working) our renovation projects.

Is it correct that with verbal contracts that a 30 day notice is sufficient?

Congratulations - you've just eliminated the vast majority of properties you choose to evaluate.

but the vast majority of mortgages are not assumable. 

Like the weather, every market is vastly different.  

Even if California will not relent on adjusting emission control standards, and the more than 1,000 supplemental workers at the Stellantis Toledo Jeep plant who are expected to rise to full-time permanent status are laid off, on balance, local incomes are rising.For the vast majority of individuals, a home is the largest single investment of a lifetime.

You might find more than one lender who won't ask for the 6-month interest reserve but he'll probably ask for a bank statement with the 10% down 4%-8% closing costs 6 months of interest just to know you have sufficient liquidity.  

This type of financing requires the projected income of the property, determined by a local expert, to sufficiently cover the monthly mortgage debt.

Since then I've had a few other contractors come out and verify the work is not sufficient let alone up to code.