The simple answer is the actor notes would go on actor pages and episode notes would go on episode pages. (yes there would need to be a notes tab for each episode.)
There is useful information that would and should be in a Notes field. I did the write up for the episode Son of the Defender for Boston Legal. There are a number of flashbacks to the old The Defender series that include dialog. The writer for that should be credited, but there currently isn't a good way to do that. A Note for the episode, solves that problem.
Stating that Simon and Simon episode 201 is a crossover with Magnum PI episode 301 (or whatever it was) is useful information, and not something a user would intuitively just know.
The "Best Known" issue is solved by using an episode count instead the current most popular show system.
It would have to be moderated, no question.

