1. The crossbow is near useless on someone who's armoured and not next to a wall.
2. Yes, ammo is common.
3.The weapon's not that common. It takes someone with the knowledge, materials, and time to make it. Wood's easy enough to come by, and plastic is almost only able to be made by mining.
And, with the concerns, you could also argue that the LAWP is in need of a nerf. The shot does 60 burn, never misses, charges, and is cargo orderable.