Question as a 600 rated player.

I like to play ruy lopez as white, and wanna try Sicilian as black (I feel caro kann is too slow).

1) Should i try the Italian Game instead of Ruy lopez (i am decently successful with it till now)?

2)Is the Sicilian a good idea at this level, considering that my opponents won't know the complete theory either.

3)Should i start learning theory and main lines for openings?

If your going with Sicilian you’ll need a opening against d.4

If you're already having success with the Ruy Lopez, there's no urgent need to switch to the Italian.

no, i would recommend having a real opening thing at 2200. Here is why. When your lower rated it gives you a small edge when playing. What is better is to play loads of games with a variety for openings so you know what to do in ALL positions except for the ones you have memorized.

I don't understand your point. How do i havea direct advantage in lower elo? And also should i memorize or not?

1) Cool, then try Ruy Lopez as White and Sicilian Defense for Black. Both are solid opening choices and it is good to experiment a little and see what openings you are most comfortable with. I'd stick more with what you want to play and not as much with what you are good at because you are likely to get much better at everything with practice and what you are good at now (like Italian Game) might not be your strength later, so it would be a waste to study an opening just because you are good with it now; I like the Ruy Lopez opening for you because you said that's what you want to play.

2) This is debatable, but I like you trying the Sicilian Defense if you like. I even have a YouTube video on this which might help you; I'll link the video in this post if I remember to.

3) Memorizing theory? No. Learning the main ideas, moves and plans of the opening you choose? Yes. My blog post on opening principles discusses this a little: https://www.chess.com/blog/KeSetoKaiba/opening-principles-again

Here is the video mentioned in the 2nd question: