You will be able to unlock extra material once you have enough coins from playing. You can get new cats from the shop and use them in the game. You can just use one cat at a time. Altering cats is simply for visual functions. They will not have any effect on gameplay. You can also unlock the other spaces in your house which will alter how the board looks, and exactly what treats you can integrate. The gameplay will still be the exact same in every room. It just offers you an option to alter how the game looks.