1. Dunno what you mean about making "new weapons" but with eud triggers u can switch a units weapon during the game.
There is a way of making a ammo and reload system but they require all 1 hit kills since you can't really tell when a unit takes a shot.
Just have a set ammount of ammo somewhere (you can use minerals or something like that) and whenever a player kills a unit their ammo is subtracted by 1. When their ammo is at 0 you can give them a eud attack that dosnt do anything or have them ally the enemy so they wont attack automatically (althought they could still manualy attack the enemy). Then when they're out of ammo they would just have to reload to get their normal attacks back.