I don't recommend Coinbase to people. They are known for lazy support, reporting your trades and locking accounts.
They are also pretty safe so if you're ok with being monitored and asked stupid private questions, your coins will probably be there when you wake up

Probably.
Yes, coinbase is the worst exchange in the space. How it's the most popular I have no idea
Out of big exchanges.
You will find many smaller exchanges with similar or even worse support.