If you don't have a professional property manager hired, you can probably expect to pay about 10% of your gross rents for vacancy while looking for a new tenant or might need to make repairs from the last tenant)10% of gross rents for water, sewer, trash, and snow removal (even if you're not running on city water, you still should be budgeting money accordingly for water because at some point, the pump in your drilled well is going to give out and you'll be left high and dry unless you have the money to fix it. 

This is one of the worst houses in the area right now since it looks like nothing has been done for years and a couple cars are just rotting in the field.

But please, make sure you allow for: what happens IF your "nice income" were to suddenly dry up!

If there’s wood siding, is it in good shape or is there dry rot?

I have 9 units (Quad and 5 SFR's all on 15 yr mortgages), everything is going really well, things are cashflowing quite nicely (Bought when the market was down).Right now, the market is dry where I am.  

The last 6 months have almost put me out of business because the "deals" have dried up in the strong seller's market.    

It's not always as cut and dry as gross rents - So having a stabilized property (proving low vacancy/delinquency over time) where you can minimize expenses and maximize rents will get you the highest possible value.In my experience, usually only single family homes are valued by "comparison approach."

I would ask for the materials you stated and if not familiar with the area of the listing I would drive the property and neighborhood and if still interested I would schedule a tour of the property.You will be looking for the bad stuff (foundation, roofs, lots of exterior wood rot, etc...) on a tour and also what state the made-ready units are in to determine what if any updating you may need to do to get the rents you are projecting

I don't see a problem as long as you give it time to dry out before installing carpet.

One place literally before the ink dried the tenants where already calling about issues.