It's not "officially" supported, but iFixit has a guide for swapping the drive on a time capsule. I used mine with a 4TB drive for years with no trouble.
Sure, but still just a single drive.
My old trusty readynas should still work i think.. probalby. Supports smd for time machine and smb3 generally. If it doesn't I might finally be pushed onto a nas that isn't discontinued.
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