Is anyone familiar with how interests are generated? I'm trying to determine the highest legitimate total of interest points. I understand that sims can have different totals, and I can swap points with magazines, but I don't know the absolute highest total that a sim can start with.

Any info is appreciated, please.

It depends on what you're asking. If you want to know the highest total of interest points supplied by the game, I have no idea. Reading a magazine makes you lose a point in something else because there's code in the magazines to do that, not because you've gone over some maximum.

SomeSimThings has a hacked object called the supersculpture that will let you set any interest to 10 points; it also has an option to set ALL interests to 10 points. So the game doesn't enforce a maximum on interest points.