I'm very interested in this areas as well since currently living in Seattle, i could see it would help a lot with getting more affordable (and creative) housing options here.I have good relationship and contacts with a large container manufacturer in Vietnam which builds and customizes the container homes. 

Find the owner, establish a relationship and go for the ask.

I need a few recommendations for an excellent realtor who specializes in rentals (and who gets a good number of REO's as well).

You have a choice of at least a dozen excellent REI experts here.

I have an investor that has shown interest and we have initially discussed terms where they receive a 15% preferred return and then we split anything above that (I know this may not be the best terms on my end but I'm interested in the process and it could be a relationship builder, plus infinite return if I put nothing in).

@Julio FernandezI would attend some local real estate meetups in your area and try to form a relationship with one of the private/hard money lenders there. 

Getting active in your local REIA, hanging out with similar like-minded investors and building relationships are key. 

You really don't want to imply an employee or subcontractor relationship here.

Looking for advice on how to handle a negative relationship with our property management company.

It may be done where they are multiple marriages, children from prior relationships or other reasons.