1) The install:
Text based/ncuses menus. Start by logging in as root, partitioning the drive with fdisk or cfdisk (i prefer the latter).
enter the command setup, and follow the menus. You can define the install down to the very package, or install it all, and several intermediate steps in-between, like installing collections of similar packages... Watch out though, there's no dependancy resolution -- so if you don't install a certain package required by another you want, you'll have to chase it down later. Most do a full install and remove what they don't want, or just take care with what they don't install.
It's a relative snap, though.
2) Setting up Slackware is all through the text configuation, with a couple of exceptions:
netconfig -- to setup eth0 and your hostname
xwmconfig -- switch the default WM when using 'startx'
pkgtool -- other install scripts related to configuration
Ease of use will be just like any other distro -- except that you have the incredible benefit of not having any configuration tools. I'm not being sarcastic here, because once you set it up by hand, you don't have to worry about losing your settings when some wizard comes along and changes something you didn't mean to. Everything just seems to "work". Hand editing an auto-configured text file will confuse you way more than the nicely commented config files included with Slack.
3) Package management is with standard .tgz -- those are precompiled tar archives compressed with gzip. You could install them on any distro with a simple 'tar -xzvf package.tgz' from the / directory. It just uncompressed the files into their proper locations. No dependancy resolution. I find this easier, because you don't encounter dependancy hell simply trying to install something simple, and there is no central database of installed packages to corrupt or confuse with "--force or --nodeps" flags.
4) Hardware detection is handled by hotplug. If there's a driver in the kernel for it, chances are the driver will load for it on boot. You can also take a look through /etc/rc.d/rc.modules (though that's mostly deprecated by hotplug) if something you have isn't working to see if there's a module for it.
Otherwise, nothing is auto-setup. Your xorg.conf file will come with a mostly usable generic "vesa" setup that should get you at least a color screen and moust support. Everything else is up to you
Slackware is really a bare bones, no frills, "just frickin' works" distro. If you know Slack, you'll know how to do it the down and dirty way in any other distro.
I love it.
PS -- edit to add that yes, you can just add a grub.conf entry to load slackware.