Don;t do partial config do the full as it is not determenstic.http://ebookbrowsee.net/2011-lightning-runmodes-and-configs-for-fun-and-profit-pdf-d414804732

Doc indicates rendition is not generated.  Check the logs & see why rendition is failing Or attach logs at the time asset is uploaded.. 

loopback interface will work.  What kind of authentication you are using?  Are you getting login page but not able to login with entering credentials?

Please note I haven;t implemented personally with any commerce integration.  Make sure to utilize AEM ecommerce api http://dev.day.com/docs/en/cq/current/javadoc/com/adobe/cq/commerce/api/package-summary.html

Since window.location working. To construct the url use window.location object itself to get hostname , port etcc...

http://dev.day.com/docs/en/cq/current/deploying/configure_logging.html

It is possible. Refer [1]. It deponds on your use case & you can use oob one like [1], saml, etc.. Or you can write custom one.   [1]   http://dev.day.com/docs/en/cq/current/deploying/single_sign_on.html

I do not know about DITA XML.  Generally use XSLT to convert from one format to other. So you need to write xslt.

The error you are posting not related to actual problem. For the error  follow.http://helpx.adobe.com/experience-manager/kb/invalidpollingconfiguration.html

Seems like required client libs are not included. If repository is small then compare using [1] & the difference will help to find the cause.[1]  http://helpx.adobe.com/experience-manager/kb/contentcompareimport.html