I own quite a few turn of the century multi-families up in Everett and yea, your 5% maintenance/capex/vacancy is low, especially if you don't plan on doing the work yourself.

I currently mortgage a FHA single family home which I plan on renting out soon I'm just not sure on what my next step should be on becoming an investor.

I am planning on buying it thru a bank loan with 20-30% dp.

The plan is to turn my current residential property into a rental.

Do you see any flaw in the plan ? 

If you plan on buying additional homes with this person, I would just let her enjoy this easy sale because the next one might be much more difficult. 

If you could strategize your plan of action moving forward and wanted to return the highest ROI possible then one could encapsulate different markets and buy at lows, sell at highs then take profits to put into a lower priced rental that returns passive income with not much appreciation. 

As a rough budget you can plan on $150/sq ft for just the building with foundation, then add on the land and site work after that, which can vary greatly depending on the depth of the well, type of septic system (conventional, mound or pretreatment).

Leave your cash with a suitable Lender and get them to agree with your plan (preferably in writing) BEFORE making Offers!

The plan is to repeat what works-absolutely.