Just throwing an FYI for you Halo newbs. Cortana has already chosen Master Chief before the events of Reach. It was for some brutal training program that was put into place because some general douche didn't like the Chief and wanted him all dead, but he and Cortana kicked it's ass fair and square.

Get with the programme, jeez...

Also, currently doing Solo Legendary. Taking about an hour per mission, though I'm only half way through. It's similar to 3 in that it just takes patience.