While i really do think the achievements dealy is pretty cool. I have to say that looking at some of these I know I had 10 pets and a bunch of tabards but have since gotten rid of some for lack of space. Filling a bank with 10 tabards, 10 pets and 10 mounts to complete these achievements takes up a whoping 30 bank spots just to get these points. My question is, once you gain the achievement do you have to keep these items to keep it or can i get rid of some to save space and still have it count?

Your pets and mounts are going away in the next build. In regards to the Tabards, once the achievement has counted them, you can delete them or sell them back.