If we have suitcases, can we check them at the museum before we go in to see the exhibits?

They have a bag check, even in the summer, tips are not allowed. They have limits to what you can bring in. We brought backpacking backpacks and were required to check them, but worked out just fine. I'd call to be sure.

There is a locker for small bags inside the museum. I am not sure about suitcases

We hadn't any suitcases, sorry 😃