The job can definitely be handled by a DIY. Proper preperation is the key. You will want to rent a tile saw(wet saw), they rent these at all the home centers by me,ie:home depot. As far as grout spacing for 12x12 tile, 1/4" is too small, 3/8 spacing is the norm right now for 12x12 tile. I have always used 3/8" spacers for 12x12 tile. Choose your grout color wisely. A color close to your tile color will expand the room, a contrasting color will define each tile. Designers say either way is fine, it's a personal choice. In a bathroom I would probably go with a grout color a shade or two darker than the tile itself. I'm remodeling a small bathroom right now where we are going to use 12x12 tile on the floor and the same tile 4 feet up the walls to give the room a larger look. Make sure you seal the grout when you completed. It's worth the 6 dollars for the sealer and a little extra time. Hope this helps.