I have a couple of recommendations.
First -- Determine if you want to fly sparge or batch sparge. Answering this question will lead to some design considerations.
If you want to fly sparge, you will need to be concerned about your grain bed depths a ten gallon cooler from Home Depot will give a nice grain bed depth for both five and ten gallon batches.
Second, with fly sparging you will need a good laundering system. You will probably be limited to a false bottom or a manifold.
If you batch sparge, you are not constrained by the grain bed depth. What this means is that you have more options for coolers and laundering systems. You can more easily use round or rectangular coolers. Also you can use more lautering system: false bottoms, manifolds, steel braids, mesh screens.
I have the ten gallon cooler with a stainless braid. I also batch sparge and I love the results.
I hope this helps.