Can I achieve a 5 mm deprojection? Would I be risking any future complications due to excess skin? (photos)

Would a 5 mm deprojection of the nasal dorsum cause problems with excess skin? no, a 5 mm Deprojection of the nasal dorsum would not cause any problem with re-draping of the skin envelope. The skin re-drapes amazingly well after rhinoplasty particularly in young people. You would probably not want to deproject your tip that much but the area above the tip along the nasal dorsum could easily be deprojected that much and the skin would re-drape without problems.

Yes, it is possible to deproject a nose that far, in expert hands. And the skin only rarely is a problem. One give-and-take from a deprojection that big is that the bridge of the nose can appear wider from the frontal view after surgery, despite a good job narrowing the nasal bones. But if the patient loves the profile and 3/4 views better, it's a good trade off.
Seems to me that the very tip of your nose isn't all that projecting, and it's usually the tip that we think about when we refer to projection. But the mid-point of the bridge probably would come down by 5mm or so in a well-performed operation. I gave an example in a link with this answer.
Another consideration is that when the nose is deprojected, and when a bump is removed from the bridge, it tends to make the nose *look* longer, as if the tip had drooped, so it's important to consider elevating the tip a bit as well, so the nose isn't too long after surgery.
How *much* to elevate the tip, or deproject the nose, or make other changes? We figure that out with morphs, well before surgery. I'd love for you to see some excellent professionally-designed morphs of what could possibly be done with your nose. Morphs could also help you identify better just what's bothering you, and help you set a goal for the rhinoplasty that's accurate for your tastes. Profile and three-quarter views would be particularly important in morphing your nose. (Side note: in my opinion, morphs should really be done by the surgeon, or he should direct an assistant as she makes the morphs. Morphs should be made with a constant eye to what actually *can* be done in surgery, for that particular nose, and the surgeon has that information and judgment best.)
Finally, remember that rhinoplasty is an exquisitely difficult operation to get right, and you should only have surgery if you are able to make yourself very confident in your surgeon's skills. The changes that your nose needs require advanced techniques, and skill that most plastic surgeons don't possess with expertise. For most noses, it's much better to not have surgery than to have inexpertly-performed surgery. Read my essay on how to stay out of trouble while selecting a rhinoplasty surgeon. And it also discusses how to take photos that are best for online evaluations.