You probably mean negative balance protection. Quoting off website "As an added safeguard, we offer Balance Protection Policy and will credit your account to a zero balance if your account goes into negative as a result of trading activity."
A demo account allows beginner to learn to trade. You can see how it all works, how much your can earn by opening smaller or bigger lots. You can try to scalp or trade in the long term. Even if you are a professional trader, you can still use a demo account to test strategies.
Of course you can. This broker provides you with 48 currency pairs including minor ones. So, if you're not fond of trading major pairs, you can choose any other pairs which you prefer actually.