What legalities do I need to know before I can start up a home-based pornographic studio and make videos?

Quite aside from the issues you have to deal with for any sort of business, you have to be aware of the federal laws prohibiting child pornography.  The minimum prison sentence, for that, is 5 years.  You would have to get verification from each person in your videos, that he or she is 18 or older, and you'd have to keep records of that verification, as required by 18 U.S.C. sec. 2257.  You will also need to look into any state and local laws that might be broken by what you are planning.  In some places, the types of businesses that you can operate out of your home are limited by the zoning laws, and it is far from unusual for local officials to use zoning violations to drive out businesses like yours.