If the mold is really bad in there you may need to pull any affected insulation out, possibly replace some of the decking, maybe the trusses are even rotting, it’s hard to say without seeing it myself but the root cause is likely lack of ventilation.

While I am definitely not against investing in places that you are not an expert in, I do believe that it would be nice to start in a city where you have some roots/knowledge.

We'll be rooting for you!

Generally, the negative behavior of one tenant is most likely the root of the problem. 

I have a single family home rental in Memphis area and just found out that there are root problems with the main sewer line from a tree in the front yard based on a video inspection of the sewer line. 

If it's a single, make sure to put in your leases that plumbing clog, if caused by tenant, shall be the tenant's financial responsibility; if it's ordinary wear/tear, or tree roots cloging the main, that's on the owner. 

My experience with construction is mostly interior, so preferably I would sub out everything to the point of root being on, then do everything else myself.

I wouldn't want to move out of state as I've been rooted here in Northern Utah.

A sewer scope is a few hundred bucks and can tell you if it’s due to vertical load, horizontal load or root intrusion.

Hire an objective 3rd party to determine root cause and recommended solution and then hire contractor to perform said recommendation.