If at all possible try to convince the client to let you run WAMP. I had to manage an IIS EE site for 3 years and it was an absolute nightmare.
Make sure you have .php set as a default document and higher priority than .html.
You may want to purchase ISAPI_Rewrite, which would allow you to use an .htaccess for any URL rewriting.
Permissions are a nightmare. ...
If that page has been added to the Pages module list, it will require a URI. And if you've left at least one other blank, then that's where your duplicate URI is coming in. Just check out the Pages module list and make sure you delete the page from there -- it won't actually remove the page entry in the channel though.
According to Gearhost docs, you can set a PHP.INI file per site. Using these docs, you can override the default PHP.INI settings. Create a file which shows the output of the phpinfo function to see what your current settings are. It's possible that PHP is set to output errors to a log file and not to display them on screen. This makes sense for a production ...
Which hosting provider do you use? What version of IIS/Windows do they use?
You can try to add a web.config file to your root
<customErrors mode="Off" />
<compilation debug="true" />
Can you force C:\path\to/webroot/folder instead? I have that in use on a Win server with EE. You might also change from Imgsizer to CE Image - when I did that I was able to remove the base_path type parameters from my plugin calls.