RAD 140 cycle of 10 mg 8 weeks

Hey i need some advice concerning RAD 140 cycle, 10mg for 8 weeks. I have never done a cycle before and i have been lifting for 10 years and always been natty. I have read that even 5 mg should be potent enough to give great gains. What do you recommend as first cycle, 5 or 10mg? and what cind of PCT should I take? Or is it necessary for a PCT?