Now to answer some of your specific questions:
Epson printers and the like are compabile, yes. It uses the same printing system that Mac OS X uses, so usually you can just choose your printer from a list (it'll find it if connected to your machine), and print as usual. Sometimes the drivers for Linux aren't quite as complete as for Windows, so there may be one feature that you can do in Windows, but not Linux. But usually you won't find this. They're getting better all the time, too.
TomTom: I'm not sure. I know that TomTom Home only has official installers for Windows and Mac OS X (Linux's major issue is that it's not massively supported commercially, yet).
Usability, security, etc.: it's just as good as Windows, and usually many times better. It works differently to Windows, so just as if you were to get a Mac from being a Windows user, you'll find some small hiccups for the first few weeks of using it.
Another note is that there are some great forums dedicated to Ubuntu, at
http://www.ubuntuforums.org
I'd ask you questions there too, as you'll get more knowledgeable replies about specific things like TomTom support. (An interesting note is that the software tthat runs inside your TomTom itself is actually based on Linux.)