Demo is important but one thing which you can't learn on demo is - emotional management. For this, you need to go live. You can start small with a micro account.
Yes!
Demo trading really helps a lot in understanding the working of the market. And it's always advisable - " Never to jump into live trading without practicing on demo account."
For the beginner, it is always good idea to start trading with major currency pairs like EURUSD or GBPUSD, so that you can observe them and get to know their pattern like uptrend, downtrend, and many more.