I use similar dividers for separating out encounters myself. It looks like the ones in your link are the same size, so it should work out ok. Lying sideways, they fit decently into the troughs of campaign expansion boxes with the campaign booklet lying on top (I imagine the Revised Core set has the same insert, though I don't have one to check). I don't label them on the top or anything so I'm not sure how well that would work or not work.

Different people like to sort their cards with different levels of granularity. Generally, you'll want to keep each scenario's cards separate. Then for encounter sets, you can either separate them each out or just keep them stored by campaign (ie, store all the Core Set encounter sets together, all the Dunwich encounters together...). When you play any campaign scenario, you'll need encounter sets both from that campaign and from the Core.

As for player cards, I just keep them sorted by class, one partition of level 0 cards and one partition of level 1-5 cards (keeping the leveled cards ordered by level). So 10 total segments. I've got a full collection and this is starting to get a bit onerous, so maybe I'll need to reconsider eventually, however for a smaller collection I wouldn't bother separating things out more granularly than this.

In terms of replayability, it mostly comes down to if you're playing for the deckbuilding and mechanics, or if you're playing for the story. Personally I don't replay for story reasons much, but I do replay a lot trying out new investigators and deck ideas. If you're mostly in it for the story, I think you won't find a ton of replayabiilty here. But if you like playing different characters and building different decks, Arkham is highly replayable. The XP/'leveling up your deck' system is such a great twist on traditional deck construction, that it elevates the replayability of Arkham to a whole new level compared to other LCGs (Marvel Champions, LotR LCG) in my experience. You will literally never run out of deck ideas to try in this game with the amount of content available right now, if that's what you play the game for.