Hi, and welcome to LQ!
Glad you found reading here helpful. :)
Now, I don't know how many THINGS here will
be able to help you, but I'm sure that one or the
other person may.
As for your question: that should be no problem
with a generic distro, iptables is set-up easily
enough, and Samba, even though it can be
tricky in some configurations, should be fine, too.
That said: having a file-server to be a firewall
as well is bad practice, and you should be aware
In terms of the belkin controller and the big HDD
it really depends on what chipset the controller
uses, and if it's ATA or SATA, and what distro
(with which kernel) you settle for.