CE-500:
1. There is no published maximum speed limitation for Thrust Reverse deployment in ANY CE-500 series aircraft. By 60KIAS the reversers should be at Idle Deploy to prevent re-ingestion of the exhaust gasses and debris picked up by the efflux.....
2. In a 500 you get a slight nose up pitch on reverser deployment after landing hence advice to push forward
CE-525
When using ground flap, if all 3 wheels aren't on the ground, then you risk striking the flap trailing edges on the runway with ground flap selected, hence advice to push forward.