The main limiting factor is that your primary residence is a singlewide.

There may be some local factors (nearby construction development or major change) influencing the owner to sell at a discount OR perhaps the owner has not been keeping up with capital improvements and the tenant base as suffered and therefore actual collections of rent have been impacted.

It doesn't factor in all the work you need to do to manage the place.

I did want to note that the $800/mo is factoring in a newer, slightly higher mortgage after pulling cash out to fund a rehab to the property.

The answer to your question is heavily dependent on multiple factors such as being a good manager of things generally speaking, how well you do your tenant screening, how comfortable you are with bookkeeping (if you are going to do it yourself), if you have a good selection of service providers in the area etc. 

I live in the Pacific Northwest, I'm a bit priced out of the market, I'm attracted to buying a duplex or fourplex in some state in the Southwest or Southeast where I can better afford to buy, I would like to move there and live in one of the units, but it seems like an overwhelming project to decide where to buy it seems there are a lot of factors involved and it's difficult for me to come to a decision.

Are partnerships on a property usually forever or do I just give them a certain amount of interest and pay them back over time?

But if it's just a house for you to live in, not an investment, then financially speaking you can't do better than living for free since the home you live in generally tends to be a wash or lose money when you factor in everything - maintenance, furnishing, repairs, etc. 

Risk acceptance and goals are the two main factors that are unique to you.

If you look at the analysts from the major investment firms, banks and hedge funds, many of them are discussing that a more realistic number for investors to expect in equities (stocks) for quite a long time will be closer to 7% and this is before the index fund expense ratio and inflation is factored in.