WRT firewalls, I just rely on my Linksys router's & don't install daemons (background processes) that aren't needed. There's a package called Firestarter that may be of interest.
I can suggest opening up Synaptic and browsing through the sections & packages. Look for stuff that seems of interest to you and install it. You can always remove it later. ubuntu-restricted-extras will install Flash, Java, codecs, &c that are useful for the Internet. They're not installed by default due to licensing restrictions. Thunderbird is available, but the default email program is Evolution, which is meant to compete with Outlook.
Lots of sources for HOWTOs and so on, like the Linux Documentation Project, Linux Weekly News, the Linux Journal. Don't miss ubuntuforums, the regulars are helpful.
 The only public-facing daemon I'm running is sshd, so that I can log in from outside. I also run fail2ban to slow down those damnable bots, since it will write a temporary firewall rule to block a host that fails logins more than a configurable # of times in a certain period.
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