I thought that i'd also pipe in and give some suggestions.
y0shi's is probably by far the best. you still use slack and even though the script does it for you, you can still learn from it. A good addition to that script would be Webmin. It gives you a gui interface to iptables which might be easier on the eyes while trying to learn. It was for me.
Another would be using Untangle. I've used a few of these firewall distro's and Untangle beats the out by far. Mainly because it includes a lot of addon's (that you can choose to install or not) that the others don't include and rely on the community to build and patch them. On top of that, sometimes you will have issues with some addon's not liking the other and it breaking your system.
Another suggestion would be shorewall. it's simple and a lot of these firewall distro's are based on it. using it with webmin would also be a good choice.
Hope some of this helps instead of throwing your mind into an indecisive state. :P