Basic questions about Debian package tools

["pt3asw@gmail.com" <pt3asw@gmail.com>]

Hello,

I'm a Debian Squeeze new user and have some basic questions about
Debian package tools.

Is it true I should avoid APT and use some other frontend or, better,
dpkg directly?
I tried aptitude, but I don't like ncurses-based tools. I prefer the
classic command line if possible.

How can I obtain the list of sources currently used by installed packages?
For example, since I have "gcc" installed, it should show "main", and
since I also have "firmware-iwlwifi", it should include "non-free",
too.
This is for checking if /etc/apt/sources.list is consistent with
installed packages.

I'm not sure if the following procedure is right for staying up to date:
apt-get update; apt-get upgrade; apt-get autoremove --purge; apt-get autoclean
Am I missing something else?

Thank you.