Again, we have the capability to do this today: we can run two fully identical copies of a simulation program on two computers half way around the world and keep the two simulations in perfect synchronization. There are a few difficulties, but they were solved in games a while ago. Starcraft solves this problem every time you play multiplayer, for example.

1. No not at all - just the input feed from the sensors needs to be duplicated.

2. Clock issues are not relevant in a proper design because clock time has nothing to do with simulation time and simulation time is perfectly discrete and deterministic.

(4,5,6): These deal with errors and or downtime: the solutions are similar. Errors are handled with error correction and re-running that particular piece of code. Distributed deterministic simulation is well-studied in comp sci. Our worst case fallback in this use case is also somewhat easier - we can just pause both simulations until the error or downtime issue is handled.

(7). This is important even if you aren't running two copies.

Running two large-scale computer systems that work exactly the same way is an hard task. Really hard. Similar somehow to keeping quantum entanglement in a large system.

Not even remotely close. One is part of current technical practice, the other is a distant research goal.