Brooks, as you've pointed out, IC previews a Visualforce page with no additional query parameters. The first query parameter should use "?id=" and not "&id=". The latter should only be used to chain additional query parameters, e.g., "?id=someId&action=doSomething". That's likely the first issue.
As for the stylesheet you're trying to include, is that set up as a static resource? The link tag you're using makes it look like it's trying to access a file named "healthcheck.css", but how is that deployed to Salesforce? I'd also expect to see it use the apex:stylesheet tag to ensure it's included in the header properly:
<apex:stylesheet value="{!URLFOR($Resource.healthcheck)}"/>
Let me know if all of that doesn't help.
Regards,
Scott Wells