Although it seems that you made a selection, already, here's my 2 Cent. If I got you right, you actually asked two questions:
(1) What other distribution will be a good choice in order to learn what else is available for a Slacker?
(2) How can I make it easier to set up the computers of my friends without having to do a lot of configuration each and every time?
Here's what I think.
(1) I'd suggest that you try Debian or one of its derivatives and SuSE. If you feel confident you might also give something like Arch, Gentoo or ROCK a try. SuSE is currently the best distro for modern laptops, because of SCPM, a tool that makes life a lot easier for roaming users.
(2) There is more than one way to achieve this.
- Set up a system with a typical configuration and make an ISO image off it. Create a bootable CD from it. I haven't done this, but it should be possible to create a Slackware installation CD that has most things pre-configured the way you want them.
- In SuSE (and, AFAIK, in Red Hat and others, as well) there's a tool that allows you to save a given configuration that you can then distribute to other machines in your network. You can even do fresh installs based on that configuration. I haven't checked it, but I am pretty sure that such a tool is available for Slackware, too. In SuSE, you can use YaST for that purpose.
- Create your own distribution. STOP! READ ON! It's easier than you might think. Just go to http://www.rocklinux.org
and start reading. One good point here: The ROCK build system is a collection of Bash scripts that run properly on Slackware. So you can build your own, customised distro on Slackware. And it's not *that* difficult. All you need is a lot of patience for the first build. On an AMD 2500 XP with 1GB of RAM it takes about five or six days to compile a compile distribution. Once this is done, updates run a lot faster. (Like in Gentoo and Arch).