The $5 tier gives you early access to new scenes of the demo when they're available, one NPC side story and one RO side story, as well as sneak peeks and the ability to vote in polls on decisions for the game.
1. Yes, all rewards/benefits are automatically retroactive on Patreon. If you join, you get access to everything from the very first thing that was posted for the tier you join.
2. Early access means you get access to the demo when it's available. Because you're not only paying for the demo - sometimes there won't be updates in a month due to the size and time it takes to write and code the demo, you'll only get access to the side stories and sneak peeks. I'm a writer, not an artist, so this isn't a commission type of benefit, it's an early access to the demo when it is available to play. Because the demo isn't going to be shared with the public until its final release on Steam, early access in this case means you're getting to play the game's scenes in development up until the epilogue.
Hope this answers you! 😊