I'm not that good myself, but I can help you with some of that.
Obviously you can kill any processes with the "kill id_of_the_process" command. To avoid those processes coming back when you reboot, the proper way is to make the scripts which launch them unexecutable. You can do that with "chmod 644 rc.gpm" for the gpm process. You can find scripts in "/etc/rc.d" and "/etc". When slackware boots, it uses "/etc/inittab" script, which itself launches "/etc/rc.d/rc.S", "/etc/rc.d/rc.M",....
init, keventd, ksoftirqd_CPU0, bdflushd, kupdated, mdrecovery, syslogd, klogd : kernel daemons, some of them might be unnecessary, but I have them too and I'm not too sure what they do.
kjournald : you chose ext3 or reiserfs during install, and you have two partitions, thus two of those running.
khubd, dhcpd : I don't have these. I have a single machine too.
inetd : net daemons, ftp, finger, time,... Those are listening on various ports (try "nmap -vv localhost"), which is not safe security wise. I suggest you edit "/etc/inetd.conf" and remove everything but the absolutely necessary.
crond : the housecleaner. To see what it does, check "/etc/cron.hourly", "/etc/cron.daily",... Good idea to leave it running unless you know what you are doing.
atd : task scheduler.
gpm : mouse utility for outside KDE, mostly useless.
kapmd, apmd : I dont have those, but unless I'm mistaken, apm stands for advanced power management. It's odd that you have two of those running.
The six agetty : normal, check "/etc/inittab".
Everything else is KDE related, and like the other poster said, try another X lighter than KDE.