What happens in the case of multiple land animation effects?
Yes, the land will be 7/7 until end of this turn, and a 3/3 otherwise.

Noyan Dar's and Celestial Colonnade's abilities do the same thing: Turn the Colonnade into a creature that's still a land and set its power and toughness to a specific value. When both effects are active, the latest effect "wins". 

Therefore, the order in which you activate them matters. If you first activate and resolve Celestial Colonnade's ability, then trigger Noyan Dar, the Colonnade will be 3/3, because the Colonnade's power/toughness-setting ability will be overwritten by Noyan Dar. If you trigger and resolve Noyan Dar first and then activate the Colonnade, it will be a 7/7.

Noyan Dar's ability has no end condition, and counters always remain on permanents, so the land will be a 0/0 with 3 +1/+1 counters on it when the Colonnade's ability has ended.