Actually, in the end I found an article suggesting I quit out and start again, but skip the restore as part of the setup. I created a temporary user, then did the full restore once the set up process was all over. Was able to restore everything without any further issues, including my old user account. Probably have some stray files using up a bit of disc space, but I can sort that out some other time. Just happy that Time Machine ended up working so well.
There's obviously some problem with doing the restore as part of the setup process, I found plenty of others with the same issue. Whether it's due to an issue with permissions or OS versions I have no idea. There was no error message displayed, the process just stalled.