I don't think big tiles make a room ook bigger (sometimes even the opposite). Color, light, contrasts and even texture does. Pick the tiles you really like and find a grout color that will look good with all the tiles and colors you pick.

Black and yellow are both very strong colour choices and I feel you'd be sick of them before it was time to change them. Black also shows marks more than you'd think. Clear is fine, but have you considered a piece of art behind clear?There are several companies that do this, imageglass.co.nz had one with tuis in it which has black and yellow. As for size are you having a range hood? If so this might affect your choice of size.

Double door or nothing I reckon! A single door pantry makes everything feel so cramped and that there's hardly enough space for my groceries.

Here is a layout indicating some minimum dimensions for usability. I would recommend you go larger especially if two people are often going to be using the space at one time. This also does not account for window space or furniture or storage.