Last 15 hour jitters

If you can help me out with some info I would be grateful for the next 15hours.

How do weapon skins work, in the game modes they are active will they form on the weapons you pick up (which would be cool) or is your skin only on the weapon you spawn with and once you change weapons the next weapon of the same type will not have your skin?

Is there a map specfically made to challenge forge world big, epic, and HALOey?