WOW, not to be mean just blunt but you have a LOT of room for improvement in everything you do you might want to read up more on dieting and what it consists of. Also one big questions, why no legs in your training routine? is it because of all the cardio?

Questions:
Am I doing too much cardio or too little?
-WAY too much cardio cut it down to 30-45 minutes a day TOPS
How can I burn more fat and less muscle?
-1)Like Tri will say interval cardio is your friend,
2)also get more sleep 7 hours wont cut it when you want to get cut get atleast 8,
3)get your diet in check--HUGE you need lots of improvement in this! start keeping a log, post your exact diet on here and we will have people look over it and help you with it Tri is a nutritionist so he can give you major pointers
Is my diet really my only downfall or is there something else that im missing?
-diet, dedication, and knowledge are key to anything you do with your body, before you hop on the DNP you should research AS MUCH as you can on it so you know what it is, how its works in your body, what possible side effects are and how to treat them don't just go throwing stuff in your body and hope for a miracle
should I do more reps per lift and/or more exercises body part?
-cut back on the amount of exercises you use for arms and shoulders 3 exercisers for bi's and 3 for tri's is more then enough and 4 for shoulders is sufficient (presses, upright rows, side and rear laterals). Throw in a leg day man, heavy squats and heavy deadlifts release more natural testosterone and growth hormone during your work out then any other exercises. Keep things short to the point and simple, heavy weights while in a calorie deficiency will help maintain muscle mass.


Really man the best thing you can do at this point is read, learn, and ask questions. Like i said post your exact diet up, we'll pick it apart and let you know what to do.

HOLD OFF on the DNP for a while and really research it, that stuff is not something to fuck around with it CAN kill you if you don't use it right, it's not some beta receptor antagonist like clen and ephedra but a toxic chemical.