That looks almost identical to what I'm going to build, based on an example I saw at a friend's garage. In his, the diagonal braces terminate on the wall about 18" up, and there is a second narrower shelf, with braces, below the main bench.
He also set the internal cross members lower than the frame so that his top would sit inside flush.
He used a router to round off the corners in the front. You can do this with your top as well.
Your moveable bench looks almost indentical to my current on, except mine doesn't have the casters.