Chain is toast, chainring might also need to be replaced. The brake cable probably needs replacing if the brakes don't work. The brake pads might also need to be replaced, and both tire tubes probably either need to be replaced or patched.
If it's purely just for learning, go for it. But that might be a lot of money in tools / parts and a significant amount of time. I'd probably buy a bike that is less thrashed.
Fwiw, you can have a perfectly normal bike and still spend lots of time learning to fix it. I'd lean towards that, I think.
Only if nobody else is present. This is more for quiet city areas where you have a clear line of sight, and nobody is even around. If someone is at a stop sign, you legally have to stop too.