Here in chicago for 2-flats I absolutely make sure I have equity in the building because there are more sales meaning more of them in the market to unquestionably tell me the real value.Every market is different so these assumptions may not hold true for 3-unit buildings in other markets but I know they are extremely popular here in chicago and easily sold even if they have some negative equity.

There are legal definitions that come from or are adopted by IRS Code, "Investor" is one of them, so is "Operator" after 6 years on BP, I've come to accept the popular term of "investor" in social interactions on the internet, how we use the term, but the true meaning remains as the Code sets out.Doing a sandwich lease is perfectly fine, if allowed by state law or it isn't prohibited, I doubt sub-letting a residence would be. 

One of the challenges with multi-family development of this size in Denver is that parking requirements take up a significant portion of your space.  

Even so, it does look like most of the increase in rentals is likely to be permanent, particularly in light of the fact that no economist or housing expect I know is predicting a return to the pattern of development and growth seen during much of the past few decades.and the biggest takeaway I have from this work, is that in growing, popular areas like Portland, even if the market shifts back toward ownership somewhat, overall demand will increase for both [ownership and rentals].

It is a great field, and the challenges are endless; however, at least in California the CPM process and experience requirements are pretty extensive.

I also remember 'peak oil' theories being very popular until a few years ago.

Can you share your challenge with me?"

I'm not sure of the challenges of having floor vents pose when installing new flooring. 

Each place comes with it's own challenges.

It will be a fun challenge to be involved in!