My plumber just installed laundry plumbing and a gas line in our utility room. 

You need to have enough money, probably in the $100-150k, amount to put the property under contract, and do the feasibility study on the property, Phase 1 Environmental, Property Drawings for roads, water sewer, and utilities, and have a completed budget so you know what your costs are.At that point you can go out and attract investors, I don't thing that developing raw land is necessarily cheaper than buying discounted finished lots. 

I've been at the property a lot in the last couple of weeks, and tenants are telling me that a group of teenagers will bust through the common entry doors and steal bikes and things in the hallway.  

I utilized 7% for CAPEXand 7 % for maintenance given recent updates .Tenant pay for electricity and gas.

That property is literally screwed.The real answer to your questions is it depends on what is common and accepted in that area.

This is common in my area/Colorado in general especially the ski towns that still allow short term rentals. 

Some guests are just not tech-savvy, so basic instructions for utilities/amenities that are difficult to navigate is a touch that is appreciated.

If she leaves September 15 and the new tenant doesn't start until October 1, then you can hold her responsible for rent, utilities, and other costs through September 30th.Don't wait for problems to happen before developing a plan.

@Benjamin Stacey so we utilized a HELOC to get into our first STR deal (different than your situation, but I can relate).

On the flip side, mass transit can help with the car issue and water/sewer upgrades can help with the utility usage.As far as single family versus multifamily, usually multifamily is taxed higher.