Thank you very much Yohan for appreciating. It really means great to us.
IF you read our post Calibration MMR Guide, you will see how matchmaking works in Dota 2. If you MMR is around 4k, there are many chances that you can meet 5k players in your account.
Also about Spirit Breaker, he is a great hero. I can also suggest you to try Axe, Riki and Blood Seeker. You can jungle or be a roaming support and because of Axe, you can get high amount of kills and assits because of his ultimate. Which will automatically improve your KDA. I think you are now ready to play your Calibration matches as soon as you reach trophy level 50.
From there onward it will be your winning only that will matter.