Yikes. Just to warn you there's gonna be a chorus of people telling you to use 'search' in these forums as most of what you want to know is readily available. I'll do a few but I'm literally on my way out the door right now so I don't have time (or an N810) to answer them all.

2.) You can do this, open the connection manager (Application Menu, Tools, Connection Manager). Click the Connection Manager title bar to bring up the menu, Tools, Mobile Operator Setup Wizard. (This is how it is on the 770 (OS2007), hopefully it's the same for you)

3.) Press the Full Screen button on your tablet. (I think it's on the top of the N810.)

4.) http://tableteer.nokia.com should have a video converter. Otherwise www.maemo.org in the downloads section (multimedia).

5.) Tap a text field with your finger (so there's more of a pressure point that with just the stylus). The fullscreen keyboard should come up.

8.) Application Menu, Personalization, Navigation. Click the "organize" button beside Applications.

10.) Sorry, nope.

11.) Most likely you can't "synch" in the way you're thinking. Your laptop probably uses a totally different suite of software. To install applications, www.maemo.org and go to the Downloads section. Make sure you pick OS2008.