Dude the best thing for you is to get in there and do it. Its natural to be scared but you get used to it. It may look like it hurts but trust me you really dont feel pain until the next day because your endorphins are going full blast as well as your adrenaline. While your getting hit you wont feel much. Theres no need for that nose guard headgear the best thing to use is a full face, I prefere the one from title, because when you compete you need to weat open face headgear and if your nose isnt conditioned it will bleed fast. Every time you damage a bone it reconstructs itself to be twice as strong during the healing process. Thats why vitamin D and calcium is important. The best way to build cardio is to sparr. When i first started i thought i was in shape because i ran 11 miles but when i got in the ring i could barely last 3 rounds. now im up to about 8 rounds of sparring and i dont do much running just boxing. Theres only so much you can learn from shadowboxing and bag work you need to get in there and do it. not in a couple of weeks i say tomarrow