How much time should I invest in learning Forex trading in order to become really good at it?

Actually, you don`t need to be an investor, all you need is to choose the correct form for cooperation with the right broker.

Like, the best way to learn about the Forex market is to start to use your skills in a practice. How to do that?

The most safety way is to start your career as an IB (introducing broker).
As IB you need to attract new clients for the broker, and as a benefit you will get commission for their activity by the Revenue Share model. And don`t worry, you can be a trader at the same time, choose demo account first, then cent and then you can choose by yourself, what cooperation with a broker is the best for you.
https://justforex.com/partnership/introducing-broker/?afm=152b31