This question is not as interesting as it sounds. All you have to do is look up the statute in effect for your location and see if the requirements are met. If the law says that prostution is defined as A and B happened when C is true, then there you go. You might need to consider who is going to bring the charge, since any crime has to also be reported and prosecuted.
Gifts have a pretty narrow legal meaning and part of that meaning is that there’s no obligation. So if you buy a girl $100 of drinks and meals on a date, it’s not prostitution because no obligation exists. If it was literally true that she owed you sex in exchange for the meals, then that’s likely to meet some legal definition of prostitution.
If you’re claiming that you’re in the business of creating porn films… did you get a business license and file business returns? Did you sell the films? Do you have the necessary model releases in place? Are you keeping the necessary identification and verification of age? If pornography is legal, these are all likely to be requirements to define yourself as a business. It’s a pretty poorly written law that says something is legal just because there’s a camera in the room.
Because these things turn on such precise definition of legal statutes, anytime you get close to the edge of what might or might not be legal, you have to stop talking in generalities. What’s legal in California might not be legal in Oregon, even if legislators in the two states had the same intent or targeted the same behavior.