Most businesses, property management or not, fail due to the lack of sales, not due to the lack of systems and phone etiquette.

Portuguese-registered businesses, businesses registered elsewhere in the EU)?

Not everyone will be successful in this business especially during times when people are essentially jumping on the bandwagon. 

I am currently a junior business marketing major with a concentration in professional sales at Samford University.

We use Hiscox for our insurance with our business, not sure if it works for property but its worth a try. 

I inherited a partnership in a 22 unit commercial building with 8 restaurants, a grocery store, a couple of personal care services, and various other businesses.

Incredibly poor business deal. 

The house sits near a freeway junction and a busy street, and while my previous rental was also close to the freeway, something about this home's elevation makes the noise unbearablyintrusive.

I would check with your CPA before setting anything up.If you are talking about referring people to local fun businesses like the boat rental, restaurants, amusement parks etc then there is no problem.

They have been managing fine, although not too busy, I guess because of the market.