Hey, I hope you're happy with your new slackware.
I *strongly* recommend... well let me put it this way: if you run your system as root, you're asking for trouble, and you'll have it. Seriously. So go ahead and create a user:
yourhost# adduser
It'll ask you a few questions, and you'll be ready to go.
Now you can set the system to go to X on boot. Linux has different "runlevels". Slackware is configured by default to not run X after boot, that is runlevel 3. You want to set de default runlevel to 4. So edit the file /etc/inittab (you can use the editor nano, for instance):
yourhost# nano /etc/inittab
You'll see two lines like
# Default runlevel. (Do not set to 0 or 6)
id:3:initdefault:
you just want to change them so it looks like:
# Default runlevel. (Do not set to 0 or 6)
id:4:initdefault:
don't forget to save the file (in nano I think it's CTRL-O, don't remember, but it should be written on the screen)
Now reboot, and it should go directly to X. I have no idea why it loaded fluxbox when you started X as root. If you installed KDE, you can set it as your default desktop manager at the login screen.