I think I would not tile the sides . 30 inches between two walls feels really tight.

Make sure your toilet paper holder does not make the space feel even tighter. I recessed my toilet paper holder to get more room, but you could also locate it further back on the side wall.

Can you decrease shower length by a couple of inches?

Tile all the way around. Nothing's easier to clean than tile, and this is a spot where you're going to have sprinkles, overflows, etc.