How many levels of tshuva? Is it a final or limitless process or it has some end?

Shalom, Thank you for your question. The subject of tshuvah is a very important one – especially at this time of year. Rav Kook zt”l wrote a very famous book about it – Orot HaTshuvah (The Lights of Repentance) which deals at length with the question you ask. He outlines there an understanding of tshuvah that goes way beyond (but certainly includes) just repenting from our particular sins. His concept of tshuvah includes a limitless “return” to a complete universal connection with Hashem. In this outline of tshuvah there are no limits to the concept – neither for the individual, nor for creation as a whole. For just as Hashem is limitless (and called the Ain Sof – “No Limits”) so too our “return” to joining with Him is without limits. You will find some excellent materiel on this at this website - http://www.ravkooktorah.org/ Blessings.