what level can I reach if I only play rapid chess here with no study?


Players who focus solely on playing games without studying chess theory or practicing tactics can still see improvement, although it may be slower compared to those who combine playing with other forms of learning.

Puzzles only expose you to tactics that you may, or may not, see in a game so they only help in very specific situations.
You can only play here and still improve, but you'll have to be disciplined and learn how to review and analyze your games. You will have to be able to figure out where you made your mistakes that caused you to lose, why you made that mistake, and how to mitigate it in future games.
Even without paying for a coach there are plenty of chess resources online that are free that can help you with things like basic opening, middlegame, and endgames strategy that would help fill in some of the gaps you have from just doing puzzles.