Before I answer, a dongle is usually defined as a device (adapter) that you would plug into a computer and will either connect you to the internet wirelessly or it acts as a was to protect software from being pirated. I will assume that the question has to do with the former (adapter to connect you to the internet). To allow for that type of dongle to work, you would need to root the Nexus 7 to do so.
With the introduction of the Chromecast dongle, you can use the Nexus 7 to cast media from the tablet to a HDTV.
Currently no. It lacks the connectivity like you could with a desktop to a monitor. On HDTV's, and along with a Google Chromecast dongle, you can "cast" some media from the Nexus 7 to the TV.
no
Yes, you need to have a working Google account to use this tablet.
There are various types of Nexus devices, but the Nexus 7 is part of that same family.
The Nexus 7 is an Android Tablet made by Google. It has a screen size of 7 inches.
Hard to say as there's little information on the subject. That being said, there is an app on Google Play (PPP Widget) which would allow you to connect to a 3G dongle/stick, regardless if you have a wifi-only Nexus 7, or one with a SIM. You will need to be rooted however for the widget to work for you.
Yes, you can use multiple Google accounts.
Yes, it has Google Play.
No, you will have to download a movie to a Nexus 7 tablet on your own.
It is a tablet.
Yes, it is available in the Google Play store.
Not really, unless you count the Google and Nexus branding as "ads".