You should have one more litter box than cats, so 3 boxes would be your best route. If you can't do 3, then 2 is the least you should have. However, with young ones like you're adopting, you might find you need several as they are like small children. When they have to go, they have to go NOW! When we first adopted Hannah at 7 mos, we used disposable aluminum cake pans and placed them throughout the house. As she got older and could hold it to make it to the box, then we gradually got rid of the aluminum pans. Just be sure to scoop daily and don't use a clumping type litter with little ones. You want to use clay.
I like to have food bowls for each cat. That way, you can monitor feeding to make sure they're each eating appropriately and one's not hogging all the food. Make sure you're using either stainless steel or ceramic to prevent acne.
For water dishes, I like to have several throughout the house in different kinds of bowls. I have oversize coffee mugs on the counter in one bathroom, a water fountain in the den, and a nice size bowl in the spare bedroom.