The first deal is the hardest, there are learning curves in establishing and working with contractors, pulling permits, and other things you may not think of so I would start connecting with people now and get your plan in place. 

By the time I was done I had spent 160k total (again including all commissions, permits, professional fees etc).

Baltimore County requires a permit and inspection for each new gas appliance you hookup as opposed to electric where you just plug it in (assuming, again the electric is already in place); no permit or inspection required.Gas in rentals, at least in Baltimore County and maybe in general, just doesn't seem to be worth it.Just some food for thought...

She costs $150 for initially getting the permit/license for my rental.

Also, check with zoning and code compliance to make sure this is a permitted legal duplex.

For newcomers to the playing field, it’s better to pay a bit more for a property in a good location than to pay bargain basement prices for a similar property in a lousy one—a common mistake for rookies.What makes a good location?

Everything about this basement apartment seems to be up to code, but I guess the previous owner didn't get any permits.

Do I need permits for that?

The remaining 5% is for retainage to make sure final punchlists are completed and all permits have final inspection and pass.

Become familiar with dumper rental permit issues and prices in your target area.