I am going to install 12" ceramic tiles for my kitchen-dining room renovation. I have put down 3/4" cdx plywood over the existing 1/2" plywood on 2x10" 16"o.c. joists. Home Depot carries 1/2" and 1/4" wonderboard 3x5', 1/2" wonderboard 4x8', and Hardie 1/2" 3x5'. I was told Hardie is a fiber-cement board and wonderboard is cementious backer. What type, size, and thickness is best. My only experience in the past was 1/2" 3x5 durock for tile setting. Lowes carries permbase also 1/2" or 1/4" in 3x5 or 4x8'. Also 4x8' sheets would line up on joists underneath and straddle plywood seams evenly, but does this matter for tile backing? Should tile backer be laid down in a certain pattern over plywood as far as the seams go? Is taping and thinsetting seams necessary or can they be caulked?