Hello Nedim,

To improve your lefthand technique(I assume it's your left hand) classic piano is an excellent way to go, since you'll be forced to use both hands a lot and learn to play the hands independedly from each other in very different ways.
Whether you need lessons or not depends of your own disciplin and how good your technique is.
Lessons mean that you are more or less forced to practice since you don't want to look stupid each time you have your lesson and did not practice.

About reading music:
Personally I usually play by ear, but on some occasions you can't hardly do without.
F.i. classical peaces of a certain length are difficult to remember completely.
It's also time saving if you need to play a completely unknown song to you.

I agree with most of us here that to give your playing a certain dynamic and emotion you better play by ear.
Also there are riscs with playing from paper..

Years ago I sat in as guitarist in a jazz combo in an outdoor play.
Suddenly the piano stopped, while immediately filling in the gab I looked over my shoulder and saw the pianist crawling over the ground looking for his music sheets which were blown away by the wind (I had big troubles to keep my face normal, since this was so hilarious)
The audiance did'nt notice by the way at all...

Another example:
About 40 years ago I wanted to play some classical guitar pieces. (Several pieces from JS Bach - like chaconne etc..)
To do this I bought the music sheets and learned these pieces note for note and by listening to Andres Segoiva.
While I am not a good reader at all, untill today I cannot play these pieces without having the sheets in front om me.
So once you learned a piece from paper somehow your brain says you need the sheet music...at least if you don't play these kind of music daily...

Overall I would say that for classic music you can hardly do without when learning a piece.

While performing you better do without sheets and play by ear, since it will be very static and will lack emotion if played from sheets.

If you play Jazz, Boogie, Blues etc... FORGET sheets.

Greetings
Fred