Important is to not use all 3 knuckles at the same time just skill one of it!
To Fortyfying:
I made some armor parts +7 without any tali. Weapons +7 with 18% tali. You have to know that you can fail everytime. Fortify or Buy is your choise. If you wanna go the safe way farm the dill for +7. If you wanna have some action, adrenalin and you can life with disappointments you can fortify by yourself. I just failed 135kk yesterday for nothing
So its your choise