Welcome! I'll answer your questions in order, feel free to follow-up with any others!
1. Chaos level is similar to Wanted level from blades in the dark. It's tracked on the Crew sheet, and it usually increased by having the Heat on the crew reach maximum. The idea is that your crew's Heat-increasing actions in World are actively destabilizing the status quo, which has disruptive effects on World's infrastructure and also makes the Administration less lenient with the crew (as they realize that you're the source of the instability!).
It's actually very good feedback to hear that there's a (obvious, in hindsight!) possibility for confusion with the regional rating for Data Structure between stable and chaotic. That's not meant to affect the Chaos level, and I could probably do better by renaming that to clear any confusion. Great question!
2. Yes! Here's a preview of the Revisionists: 
3. The MEM system is designed to give flexibility to the characters. The core system of the game (blades in the dark) was designed to run heists, and heist fiction (especially cinema) is often about the characters showing us their cool equipment right at the moment they need it. In-detail planning often happens off-screen. Another example of this principle at work is the system for Flashbacks, which let you back-fill in clever planning on the part of your characters in the middle of the action.
The way MEM is represented in Hello, World is that until a PC locks in their MEM slot by announcing what they're carrying with the slot, it's quantum: a piece of gear that their character has planned for and knows (or suspects) they'll need later in the score, but since we're discovering how the heist goes as it happens, we the players don't need to plan that stuff out ahead of time. In Hello, World, depending on how you envision the setting, it might actually be quantum data that turns into the item, or information that is downloaded just as needed, but that's up to you!