Just install everything on the machine and then just slowly remove all you don't need
I'm just doing it. Mostly check that in /etc/rc.d/ there aren't any "futile" services running.
For example if you have sendmail running and your not going to use it, just type:
chmod -x /etc/rc.d/rc.sendmail
Then you might check your open ports with nmap. Just type nmap localhost and it tells which ports are open. Check that you know why each of them is open and close them if needed.
Hope this gets you started
Nice of you to choose Slackware. Excellent choice