When we first became interested in buying property in PR, we considered it as a business investment. We currently have an LLC operating college-rental units, and thought that our LLC might purchase the property and do business in Puerto Rico. This it turns out is not uncommon, but businesses incorporated on the mainland are considered foreign corporations in PR, and must secure a license to do business. If memory serves, the fees were not prohibitive, perhaps $100.
Of course, if incorporating on the island is a possibility, this will likely cause you fewer headaches. On top of that, Act 20 may very well apply, provided that your business "is engaged in an eligible service for export."