Your loan agreement will ultimately dictate what you can and can't do with the property. 

(at least for the first few properties) I do not need cash flow in the short run but my ultimate goal would be to retire early from my investment properties.

And most times, if you have that grind mentality, they will feel somewhat threatened by you ultimately becoming their competition (unless of course they are retiring or getting out of the business).I hope this somewhat helps.Georges Franco

The ultimate goal here is to retire as soon as possible and not wait to grow equity over 5-10 years to be able to retire. 

Many new investors gravitate towards the lower cost SFH's because they are easy to finance, abundant in many markets and are the easiest pathway to completing the BRRRR  which most new investors view as the ultimate real estate success story. 

I see (and endorse) the analytical, structure-side of what you are saying, and ultimately, like I said before, I appreciate your post.

But ultimately, the terms proposed can be changed at any moments notice.

This is a summary of learnings from a recent project I personally completed.  
Steps involved:
1. Buy a home with a large backyard
2. Get permits to build a detached ADU (DADU)/backyard cottage in the backyard
3. ...

Lowering the primary mortgage payment is the ultimate goal, not acquiring new properties. 

Ultimately, my goal is to scale my portfolio and purchase a second property within 1-2 years after graduating.