Not at all. I won’t call it gambling in any case. You do a lot of research and analysis while you trade. Gambling doesn’t require any effort. Its juts your luck and trading is far from that.
Diversification is undoubtedly good. It allows you to spread risks among various assets and you can even set off losses from profits on other assets in your portfolio. Investment in just one stocks makes you subject to a lot of risk. Imagine what happens if the company shuts down.
For practice!even after years of experience you should use a demo account for testing your strategies. Many experienced traders do that. The importance of a demo account is far more than just practicing.
I maintain a trading journal and make it a point to not deviate from my rules when i trade. This way i am able to avoid some unnecessary trades as well. Without it its hard to be disciplined for me.