Most people that scale also choose one strategy to start with and scale in.

Hi. I own a duplex property (I do not live on site) and I'm renting out the 2 bed/1 bath back house. I got three applications today. All of them are financially qualified and sound: 1. Single woman, mid 30s, small dog...

Also, even if it's true that is has been working to avoid the DOSC so far, my understanding is that any "outright sale, deed, installment sale contract, land contract, contract for deed, leasehold interest with a term greater than three years, lease-option contract or any other method of conveyance of real property interests" can trigger the DOSC (quoting the bank definition of transfer or sale), meaning that banks could still call these loans due despite the executory contract/land contract if they so choose. 

If you decide to exit real estate entirely, just make sure whatever investment path you choose aligns with your goals and risk tolerance.

To answer your question about maximizing profitability: I choose to invest for equity and forced appreciation.

Last thing I'll say is a quote that stuck with me, "Choose Your Hard".

Rent control in the bay area can be extreme as many areas have rent control in excess of the state mandated rent controlIn general experience RE investors are not choosing to add a single ADU in single family zoned areas.  

However, between the much lower mortgage interest rate in Europe and a better tax treatment in the US, I'd choose the former.

Our end goal is to be in a position where we can be very selective and choose the clients and properties we work with so that doesn't happen.

State your legal theory if you choose to take an adversarial position.