I have Civi for WordPress installed on the main domain of our site and have multiple other WordPress installations on various subdomains. To streamline things a bit, I'm preparing to enable WPMS. I was wondering if there are any special considerations I need to make to ensure Civi doesn't get broken somehow. It doesn't need to share data with any of the other sites.
You only need to be aware that Civi doesn't fully work with WPMS as yet. You can Network Enable it, but the Civi backend will not function as expected on sites other than the main site. There are workarounds, but since you aren't using on sub-sites then you should be fine if you just enable it on the main site.