I would guess that the 237MB "used" is for the data structures required to implement / manage / maintain the filesystem. Block lists, inode equivalents, etc. Normal overhead.

For swap space many, many people say NEVER PUT SWAP ON AN SSD. I don't know much at all about how Microsoft does things, but if I had swap enabled on my Linux machines (I don't, because they have plenty [8GB+] of RAM), then I would definitely put it on the SSDs to avoid major slowdowns.