Just purchased a new alpine headunit after my stock navi is no longer functioning. I would like to utilize the new head unit's mic. where is the best place to mount this?

Also I have a backup camera that was just hooked up to the trunk DVD unit. but now that is no longer operational, i would probably need to route the wiring all the way to the front of the vehicle and to the back of my head unit. What's the best practice for doing this?