It won’t cause you harm, that’s for sure.
But really, you don’t want to get ripped quick. A quick rip is a great way to get injured and ultimately delay your training. Take it solid and take it slow. 100 pushups in the morning, 100 at lunch, 100 in the evening, and push the numbers up as the sets get easier will certainly give you upper body advantage. Even one set of X a day is enough to get started.
There is no set number. Just go until your body can’t go no more, then squeeze out one more. Write this number down. The next day, try for that number plus one. Keep going. If it hurts, stop doing it! Try again the next day.
Your question reminds me of the 100 pushups site. It’s a solid site. Try using its techniques if you need a hand.
And I’m not here to nag, but you really have to cut out any junk food you can. A lot of junk food is not what good strong men eat. You are what you eat, your muscles need vitamins and proteins and all sorts of things provided by a variety of nutritious intake. Keep the junk food for a snack – go out once a week, have a junky dessert (a cheesecake) over a week’s dessert. But if you eat crap, you are hindering your own progress, and will never get ripped fast. Some people can eat crap and have muscle. These are exceptions to the rule and are caused in part by their metabolism, which no one has control over. Solid trained ripped men eat a balanced meal often high in protein. There are books that have eating plans for muscle building optimization. Go down to the bookstore and ask around.