Spawning is handled by adding all 4 as a rare spawn to any “enemyanimal” spawn groups. It looks badass to leave them in though, especially if you get one to the knee. On dedi or MP, other players can remove them for you, but Xyth has not tested that yet. Those arrows can be removed by the player but you may need to change view sometimes especially if its stick into your butt. The archer will put arrows into the player. They are not over powered and are not tough kills except for the boss.
Some randomly shoot more than 1 projectile per shot, which is also adjustable.
Change the ammo speed and/or the SpreadDegrees settings in xml to adjust. These may need adjusting, but are set at various ranges and are pretty accurate. Each has a ranged weapon with xml configurable properties.