Hey Christine,
I would suggest getting consensus around the goals of your nurturing program to figure out the best strategy.
E.g., (rhetorical questions) who are the leads you are intending to nurture? How did they get on your list? What problem are THEY trying to solve? What behaviour are you trying to encourage? What types of communications would best achieve this?
From a technical perspective, I think you could combine your ideas in a variety of ways using an engagement program.
The program could start everyone at the beginning and drip out your evergreen content. If you have some content that is time-limited you could enter it into the stream and make it availble for a limited time. Later leads wouldn't get it.
You could have it be endless by adding new content and also have an exit program based on engagement (e.g., if MQL remove from stream, etc.). You could also have different streams/programs for topical areas to make it more relevant, if the volume of each segment made this worthwhile.
I would generally recommend having an evergreen program that leads go through and receive a consistent experience. This way you can test and optimize to figure out what works best, as well as adding new stuff at the end for leads who are exhuasted.
But again this could vary depending on the business scenario.