Key to multis in philly is to 100% verify that they are legal.

Now this is probably not legal in most places and risky, and creates a full time job for you. 

Based on the location legal description, the zoning department should be able to tell you what you can and cannot do when it comes to removing the existing home and placing a newer mobile home on the land. 

The first is just the mortgage payments which typically cannot exceed around 28%.Then your mortgage payments plus your other debt obligations which typically cannot be greater than 40-48% depending on the lender.

To figure this out, we need to know the following:- How much debt, if any, do you currently have on the property?

Have them sign an actual lease and then send them a legal 30-Day Notice to Quit (eviction) on day 59 of their stay.Doing this, will allow you to quickly start eviction process if they overstay and don't pay.

I told her I would comply with whatever was legally required, but I'm not yet sure what that is, so I'm trying to find out.

I make $100k a year and only have one vehicle payment for total debt. 

If the in-place rents generate don't generate enough cashflow to cover your debt service, you'll want to plan to bring additional equity to the deal to cover the shortfalls.

High credit means this is someone who pays their debts.