hi! I thought id respond here to your question, sorry on the late response by the way! i believe it shouldnt matter whom donates the items, as long as 50 are donated, of course im not entirely sure how playing as an ordinary player works, so i think you get the PWP suggestion for the Cafe as the mayor character.
also you should get rid of whatever you dont want/need, you can always get it back later, most people dont have a need for common stuff like flowers and trees