Porcelain Tile 12"x 12"

This is continued from April 8th.
Side entrance porch tiling over cement closed in porch.
cold in the winter burrrrr, the area is 5' 3" x 13' 3" I'll have a
6" x 36" extension
exposed out side under the threshold ?
I found the exact tile I want 12" X 12" Porcelain. a rating of 5 was told this is best. Their price $.88 ea
I have the grid all layed out and want to make room for the spacers.
what would you recomend 3/8" or 1/4 "

Deck hand