All the *options* (UI settings, checkboxes, etc.) are set in mirc.ini, so you only need that file.
Keep in mind that like Bekar mentioned, there are other settings you may want:
- any script files loaded (will be referenced from mirc.ini)
- your address book settings (ignores, auto ops, etc) will be in control.ini
You may also want to copy:
Because certain mIRC commands do modify those files.
If you just want the UI settings though-- mirc.ini and that's it.