Q: An initial question is... with so many games focusing on nWoD, and you guys using GMC rules for it, will players need access to both sets of material?
A: Both would help, that's for sure! But I plan on doing up as comprehensive a marriage-equivalency set as possible (with HR's help on some of the math bits if needed) to make sure that folks who are familiar with GMC/new but not old, have a decent chance of understanding what's in place.
Q: How easy/hard to you expect knowledge of the old theme be for people - since I assume the majority of the potential playerbase won't have played MtA in many, many, many, many years?
A: The uncertain Truce between the three factions (Traditions, Hermetics, Technocracy) and the SPACE CITY are a bit of a toss-up than usual. Someone who doesn't feel comfortable with the older setting and theme can still play, just someone who's newer to being a Mage and thus not all caught up in the previous Ascension War situations. I don't see a problem with writing up This Is What It Means To Me as well on some pieces, if only to help establish how I plan to handle decisions.
Q: What, other than mirrors into other realities, keeps the sleepers from figuring out what's going on?
A: The Mages themselves. If the Sleepers realized there's a great big magi-tech dome overhead, and that a computer (Control on Avalon) was handling the nitty-gritty mechanics of their world, they'd Disbelieve. The paradox would rip the city to shreds. Goodbye, last remaining population! Goodbye, any Mage who can't think up a spell fast enough!
Control will also handle the nitty-gritty of people 'traveling'. An NPC who wants to visit LA is going to end up tucked away in a sleeping-pod for a week, and then get deposited back into San Diego with a set of memories about how that trip went. Food moving in and out, how much, to which stores, etc.? Handwavium Control. It's a computer (with a bit of extra story fluff added in) so that it can take care of the level of detail that a person couldn't contain in their head.
Q: What happens when someone drives too close to the city limits (edge of the world)?
A: See above! Control takes over.
Q: Is the city now orbiting the sun as it floats in space?
A: I had personally imagined it more like a bit of tether hooking the city-chunk down to where it used to be. Now, that might not work exactly as-stated (Why can't the Nephandi climb the tether and get at our Heroes, ES?) but that's the general idea.
Q: How do mages explain the changes in the constellations that would cause?
A: Magi-tech dome says there's no change at all. Same with the weather. Did you wonder why San Diego is so pleasant all the time? So sunny? So warm and so rarely more than a bit of rain? Now you know!
Q: What about spatial debris? (e.g. Pluto got reduced from planet to dwarf planet because it doesn't have enough mass to completely clear things from its orbital path. How do mages deal with spatial debris the city will come into contact with?)
A: Magi-tech dome, though I'm not agin' using that as a bit of plot if the time seems right for some 'oh god what about the dome we're all going to diiiiiie'.
Q: How far away from earth is the city?
A: I haven't thought about that at all! Does it matter? Or is it just curiosity? If it matters, I'll think up a number. Heck, I might think one up anyway just so it's there.
Q: The other cities?
A: Plot-distance. Do you want to go explore a dead city to try figuring out why it's dead? Maybe score some phat loot? Sounds like a plot to me!
Q: What happens when Mages use common powers to access the Shadow/whatever other 'parallel' reality? And what lurks there?
A: This is still under discussion, especially since you reminded me we need to think it up. Thank you!