You have a lot of questions.

Might want to try the IRC room.

I'm going to link you to my post about OSes, I hope it helps. Also continued here. Despite the bad grammar, some slight factual inaccuracies, I think there some good points in there somewhere. Full thread here.

To be clear, you really aren't likely to get a virus on these devices as they run Linux, are ARM, and because you stick to the official & official-unofficial package repositories.

I suspect it would be possible for a Flash virus or python script to do damage but the chances of that approach nill. You might install a buggy package but nothing malicious.

And if you have any problems, it's easy to backup, flash the device and be back up in running very quickly.

Oh and http://wiki.maemo.org/Category:Users might help too.