As for other parts to have on hand just in case something breaks, the M&P pistol armorer manual have the following service interval.
At 5000 rounds replace:
- Slide stop
- Trigger return spring
- Recoil spring assembly
- Magazine spring and follower
At 10 000 rounds replace
- Slide stop
- Trigger return spring
- Trigger bar assembly
- Recoil spring assembly
- Striker assembly
- Magazine spring and follower
At 15 000 rounds replace:
- Slide stop
- Trigger return spring
- Recoil spring assembly
- Magazine spring and follower
At 20 000 rounds replace:
- Slide stop
- Trigger return spring
- Trigger bar assembly
- Recoil spring assembly
- Locking block assembly
- Locking block assembly
- Magazine catch
- Striker assembly
- Striker block, spring and spacer
- Magazine spring and follower
- Ejector