HI

When I stack my buttercream cakes, I have a very hard time with the bottom edges. Every time I lift it off the stand to stack it, the edge cracks and sometimes sticks to the  plate and breaks off. I usually have all tiers in the cooler overnight before i start stacking them too...

1st off, b'cream should not 'crack off".  Sounds like you are using a very dry/crusting recipe.  If the cake is on a cake circle/board it will not stick to the plate so be sure to have the cake on a cake circle just a bit smaller than the cake -- like an 8" round cake on a 7" board.  Slip your off set spatula under  to lift the cake  enough to get your fingers under it.  Every tier needs to be on it's own board for proper support.  Dowels in the lower tier hold up the cake so if there is not a cake circle those dowels will just push through the cake and not hold it up. 

I always run a sharp knife under and around the whole cake before I transfer it.

I like to use my large offset spatula to lift the cake and help place it.  It also works well to reposition, if necessary.  I usually run a small bead of buttercream around the joint between the two cakes and smooth it with my finger.  Any damage is repaired at the same time.