What damage and unexpected issues should I plan in.   

My first fix and flip became a buy and hold rental - unexpectedly.  

If its only five units I would go with one of the private outlets even if it cost a point or 2 much much easier are you going to buy to hold for income?

For example, the older the house the greater the potential for unexpected issues.

Be as specific as you want, but be open to recommendations from your GC - maybe they can get you a discount on fireclay tile instead of porcelain, or they think an epoxy grout will be more durable than a sanded, or whatever.Of course, if you're just painting and gluing down floor, and you know a good electrician to put in a couple of new outlets, do it yourself as long as your permitting office allows.

As well as people buying and being forced to move unexpectedly after closing. 

Just keep in mind, either way you go, with only $1,200 a month of income be very careful about any unexpected expenses before you are able to rebuild a nest egg. 

Only one outlet in the house even has a place to plug in a ground.

If they want out let them go as its not worth it for anyone. 

When you talk about $66/door you could have one expense, one unexpected (low-dollar) plumbing repair, and you've lost your entire year of cash-flow.