Instead of any forced rules I think it would be best to start off with “soft” rules or nudges, like pop-up messages the first couple times a new user clicks “Agree” and renaming or minimizing the importance of Research Grade. If it turns out that people ignore those then I can see justification for implementing something hard.
Although not having the Agree button for 3 months might help to convince users who have already been here for a while, and wouldn’t have as many negative consequences as other suggestions I think.