Error 3 means its Kaput mate, you won't be fixing that. Very very common. Most units end up with error 3 code when getting a bit older. Never heard of only being able to manually tune radio in but there you go.
Best thing to do IMO is get a nice double din aftermarket stereo in there. Maybe a touch screen with sat nav?
Yes the head unit is very easy to remove. Do a quick search on YouTube and there are many videos demonstrating how to remove it. Little piece of advice, tape up the centre console before removing, it scratches easily.