Is it only required to unlock all 25 items on the Rewards menu?

The current record run goes thru level 30 on Knockout Challenge, which gives the end credits, but that appears to have been done only to unlock the reward. He then tries for the level 50 reward but gives up and buys the reward, so is it required to reach any specific level of Knockout Challenge or can you just buy the rewards for it?

He also levels an Amiibo to max level, which again may just be because there is a Reward for it, which can just be purchased with coins instead.

If a mod could please provide a definition for All Achievements/100% I would appreciate it before I begin working on an improvement for the category.