I use mana per kill items for fast regen during the battles and i would like to know when should i start to use Intelligence armor + weapon . Is it level 10 the moment when i should switch from mpk to int or i should wait to reach higher levels ?

It depends on what class you are. If your a mage and guardian inteligence is the most important so use them asap!!

wait until level 25. Until then use mpk, heal charm, and a staff with good EE/Damage

Its the fastest