I just got an N810 too! Very exciting. Though I've had an N800 for several months, so I'm not new to the platform.

Most of what you'll need to do the stuff you want to is available from the Maemo extras repo -- I'd recommend digging there first before looking elsewhere.

I agree with the above list, though I much prefer the built in app for chat (given the well-integrated presence system) over any alternative (such as Pidgin). There are a couple of plugins available (from another repo, contradicting myself -- the Collabora Haze repository) that give the built in app access to chat protocols (MSN, AIM, Yahoo) that it lacks out of the box.

For a list of repositories, see gronmayer.com/it.