Sometimes we like to shake things up or just see how other people do things. Currently I have a super simple set up, hardcover Moleskine notebook with a fountain pen. Thinking about changing it out when it’s done due to minor bleed through.
I also have medium size hardcover moleskine notebook but I'm using a Pilot Metropolitan gel pen because, like you said, a fountain pen bleeds a little. I'm thinking about getting a Tomoe River notebook to use the fountain pen, they're always recommended.
Tomorrow River is really good for fountain pen, but I heard that something happened with their production line that the newer batches aren’t as great anymore for fountain pens. I’m not sure how factual that is since I haven’t heard much about them not handling fountain pens, but it should be fine for a gel pen.