This is actually a pretty brutal workout because all of these pushup variations do something for your chest. This is what you call a total chest workout. I'd say start out with 8-10 with each variation. You have to build the tolerance to really get this workout in. Peep it:
Standard (15 reps)
Wide (15 reps)
Wide: hands pointing out (15 reps)
Close (15 reps)
Hopping (15 reps)
Alligator Crawls (15 reps)
The key is doing about 3 rounds of this. If you feel like this will get you too tired, just try to lower the rep and build for weeks to come. Enjoy!