The first being - don't bring your friends or family into the mix :)Since it sounds like you're pretty solidified in your friend moving in, and it could be a good first roomie, so just to get your feet wet... i'll double down on Laura's advice - do a lease, for the legalities, but i also highly recommend some sort of written (we call it a) Room Mate Agreement.

Obtaining your realtor's license to get your feet wet. 

My recommendaiton would be to build the ground level as a "wet basement".

@Sebastian Tamburro you're going to get advice/offers from numerous people trying to profit off you - be careful!

Wet spot.  

I responded back with numerous questions regarding the Scope as I really want to know where my money is going.

It only looks clean when wet and I have tried everything !

Prior to these neighbors, the unit above was occupied, and we never experienced any problems.We’ve spoken to management multiple times, but they’ve been completely unhelpful and have taken no meaningful action and even told us that we are making the noise up, inspite security having been to our apartment numerous times wittnessing the noise. 

Property management is one of our core services, and we've worked with numerous property managers over the years.

We have expansive soils here (clay that expands when it gets wet) as well as some older cast iron lines and even some orangeburg so it's common to see sewer line issues (often just some tree roots that need to be cleaned then the line re-scoped).