I have seen some designs which have deep tiers consisting of 2 cakes and covered in fondant as one whole tier. Do these cakes have seperate boards and supported by dowels or do you treat them as a normal single cake?

I'm still new at his but I've seen it done both ways. I've only done one 2 tier, I did not use a seperate cakeboard for the top layer, I just glued it with icing. Good luck with your cake!!

I always use cake boards and dowells for each tier. That will prevent the upper layer form sinking on the bottom cake or sliding off.