My concern with this is it is hard to predict future value of property and I don't want to invest based on an assumption of appreciation.

I can't predict the future for sure but I can get a sense of what I think is reasonable. 

It is impossible to predict.

I'm going to predict that the neighbors will not back off.

I have not had any luck with that and also me looking at several properties and being actually client that you have to work for was not something the realtors wanted.I am pretty new to real estate in US and for past 12 months have worked with 6 different realtors just to find that really the only benefit that they brought to the table was the legal documents and confidence that there is a shared liability through realtor looking at the deal.Maybe it is that I just have not found good investment or due diligence oriented realtors here in Portland, OR, but I felt like none of the ones I worked with had an idea about bargaining or how to form an offer based on predicted remodeling/fixing or income generation or even market conditions.

Have you talked to management companies to see what their actual cost and rent predictions would be?  

With 20, things will likely average out and you are more likely to hit the "average" vacancy rate (which can be predicted).

I predict that by the end of Obama's first term.

I've also assumed an equal cost for unit #4 as my current rent, as I am going to move into this - if I rented it out externally, I would predict $1200 -$1250 in rent based on comps.ExpensesI'm assuming all other expenses are in the mortgage.

At this point, he has 25 paid for properties and just built 4 sets of duplexes with a loan, pumping all proceeds back into those duplexes and that they generate, in 7 years his prediction is they will be paid off.