@Vashti Green
If you can purchase a 4-unit for $140k that has $700/mo rents per door, then grab it! That's a great return!
However, a $140k property that brings in $2800/mo isn't likely to be on the market very long...or there are some other variables that keep buyers away. Most likely the property has one of the following:
A. significant need of major repairs (roof, HVAC, electrical...)
B. is in a bad neighborhood (high vacancy, turnover, and/or crime)
C. tax lein, or other financial problems
D. a combination of the above.
Remember that you're going to have to live there. If you and your husband don't feel safe, then it might not be worth the trouble.
As for your long-term plan, just remember that you can't use the FHA loan more than once, unless you meet a couple exceptions (forced to move due to job relocation, growing family...).
Remember that you can factor in closing costs as part of the price negotiation. For example, offer $138k with the seller providing $4k in closing costs. That would reduce your cash requirement for closing.
Don't worry about paying rent yourself. That's just handing over 10% more to your Property Manager that you could keep in your pocket, and doesn't give you anything extra. I guess you could call them to fix stuff when it breaks, but then they're just going to charge you even more to coordinate the contractors.
As far as the price of the rent, I've read several times on here, and it makes complete sense. You don't set the rent, the market sets the rent. You have to be competitive in regards to your neighborhood, amenities, location, and other owners. See if you can get a peek of the financials from the selling agent. Sometimes they won't provide them until after the unit is under contract, but sometimes you can also access the rent history through websites like zillow (I'm assuming that's fed through MLS, but not sure).
Hope that helps.