For factory pistol ammo (no P+) 14lb is standard weight. If your reloads are milder you can go with a lighter one. How much lighter depends on ammo.
Shock buffs are not needed when the recoil spring is properly calibrated to the ammo you shoot, for example 14lb spring and factory ammo. The lighter the spring you put in the more you need a buffer. It will not harm your gun regardless but may impaire slide locking/unlocking. To minimize this possibility get the thinnest one you can get or shave a regular one to a half of its original thickness.
Two piece guide rods are intended for bull barrel guns with reverse plugs to make take down easy. There is nothing wrong with them in barrel bushing 1911 guns but two piece feature is useless there,