
This question has been answered by sottwell. See the first response.
I'm usually doing the same thing by just leaving all the "normal" sites of a website unpublished and then setting site_start to the coming soon page.
Sure, a manager user with permission to view_unpublished (what you have as admin user) can always see the resources (also in frontend).
In the System Settings, filter by area "site" and set the Site Unavailable page to your resource. Logged-in Manager users can still view the whole site.
In the System Settings, filter by area "site" and set the Site Unavailable page to your resource. Logged-in Manager users can still view the whole site.