RE: NAV and SharePoint 2013
I just completed some testing this week concerning this. The NAV 2013 Portal Framework will not install into an environment that uses SharePoint 2013. At this time, it only works with SharePoint 2010 Foundation or Server. The install checks the installation version of SharePoint. It doesn't matter if you have a SharePoint 2013 site using the 2010 experience.
As for compatibility issues of NAV 09 with SP 2013, no specific testing was done but 2013 was installed into a NAV 2009 environment without issue and both operated fine. No custom integrations were performed but there isn't a framework to install like with NAV 2013.