One stupide question, if i create a new my crysis account ( when i'll be better if it happens one day ), to restart with blank stats, how will it happens with the dlc i bought on this account ? will i have to re-buy those dlc's or will they follow on the new account ?

It's tied to a single account

ok, so i won't buy new dlc, and due to the fact i won't ever improve myself , i'll continue on this account

It's tied to a single accountYou would also lose Limited Edition content. Further, to make a new guy whose loadouts, unlocks, etc are truly "clean and fresh", you have to make a new profile in Singleplayer and make sure it is selected when you play that character.