If a Monument has any +1/+1 counters on it, those counters will remain on the permanent after it stops being a creature. Those counters will have no effect as long as the Monument isn't a creature, but they will apply again if the Monument later becomes a creature.

A Monument can't attack on the turn it enters the battlefield.

Each Monument is colorless, although the last ability will make each of them two colors until end of turn.

Activating the last ability of a Monument while it's already a creature will override any effects that set its power or toughness to a specific value. Effects that modify power or toughness without directly setting them to a specific value will continue to apply.