Masturbation is normal. Every man does it. Watching porn while doing it is also normal (why else is it a multi-billion dollar industry in the US alone?). I agree that as long as it is not the only thing you want to do, you're fine.
How often you do it depends on many different factors. Age, sexual drive, personality, and general health all factor into it. For a normal, healthy male in his teens and early 20s, I masturbated or had sex if I was in a relationship 2-3 times a day. Today, now that I work and am more mature and my hormones have (finally) settled down at 28, it is more like 1-2 a day, either alone or with my wife. Older men, maybe once a week.
Masturbation isperfectly normal as is one's need for sexual stimulants while doing so. It is perfectly natural and although most women don't admit it we do it too. It'spart of a healthy sexuality. Your good, as long as it doesn't take over and it's all you ever want to do ;)
Masturbation is not wrong in any way. its good to keep attuned with your body. as long as that or porn doesnt start taking over your life and becoming an addiction then you have nothing to worry about :)