Can I replace Apache with a different web server?
You can install other web server software like, for example, nginx using brew.

Personally I would just turn Apache off, I wouldn't try to remove it. Off the top of my head I can't think of any places where the OS depends on it being there, but given that it is installed as part of the OS, if you remove it there is a good chance that a future software update will just reinstate it.