Lastly, it looks like you have some type of paneling halfway up the wall.

My biggest concern so far would be it is currently all on one electric meter with a fuse panel.

If you don’t want to spend the coin on this type of inspection, I would just accept the up front cost, and find a local licensed electrician to upgrade the panel (check wiring and outlets) for you.

He told me that a new panel and rewiring alone would be at least 5 grand ballpark.

We have solar panels on one of our rentals.

If you build out from scratch (which rarely makes financial sense because you have to abide by new building codes with fire sprinklers and solar panels), you may want to check with an attorney because I haven't been able to get a clear answer if you can do that with existing tenants because of yard space.

I have used the sound reducing panels (just a different brand) before and it does help but it will also be a considerable investment to make a real difference. 

If I included utilities, probably ~$800/mo or $3,200 gross.My main concern with it is that it has one furnace to heat the entire place, one electrical panel, one water meter, etc.

I actually met you at your plant this summer when I picked up a trailer load of panels for a project of mine. 

It's fairly common although I would go ahead and cover it with something else such as wall paper or those fake brick/wood panelling boards they sell at Menards