Hello, Iars.
Your writing is good. I can understand your Japanese. If you want to write any sentence in Japanese, you might want to use "masu" form as piotr said. And boku you wrote is casual (informal) word, so you can talk in school, with friends. But in work or formal sutuation, I suggest you should use "watashi".

Boku wa Tabete imasu ( is this right ?i'm eating now?) = Boku wa ima tabete imasu.

Q) anatawa nani wo tabete imasuka?  (What are you eating?)

A)  (watashi wa ) sushi  wo tabete imasu.

Watashi wa ima suhi wo tabete imasu.

Enjoy learning! (^^)/