Would I plant them right next to each other, or one space apart?
Also, if I have 4 Attack EVs, would one Kelpsy berry get me down to 0 EVs, or would it reduce my overall stat?
To answer your first question you plant them right next to each other. Then you have the chance that the Kelpsy berry will be growing on the tree with either the Persim Berry or the Chesto Berry. To answer your second question it would lower your overall stat. Their are certain berries for lowing EVs I just can think of the name for the Attack Berry right now.