1) Minimum size I'd got for would be around the 8GB mark. A typical Linux install is around the 5GB mark and you'll need some space for your home directory.
Not sure about the differences between USB 2 & 3 - obviously 3 is faster.
2) Slackware defaults to command prompt on first boot (you have to edit /etc/fstab to get a GUI on boot). The issue you might face is that the distros are gradually diverging. If you're going to be using a distro with systemd in it then Slackware won't help that much as it doesn't have it and there are now quite serious differences emerging in how run levels are controlled and if you're going to learn the CLI then you'll need to get the hang of runlevels. Any distro can be told to boot only to the CLI so to be honest, if you're going to be using Suse then stick with Suse (a headless Suse install is quite easy - it must be because I managed it and I am not that technical a sort of person). The openSuSE forums are well populated and extensive in their scope.
3) www.linuxquestions.org (http://www.linuxquestions.org) is a great place for highly technical help and probably has links to more educational resources.
Hope that helps some.
Not sure about the differences between USB 2 & 3 - obviously 3 is faster.
2) Slackware defaults to command prompt on first boot (you have to edit /etc/fstab to get a GUI on boot). The issue you might face is that the distros are gradually diverging. If you're going to be using a distro with systemd in it then Slackware won't help that much as it doesn't have it and there are now quite serious differences emerging in how run levels are controlled and if you're going to learn the CLI then you'll need to get the hang of runlevels. Any distro can be told to boot only to the CLI so to be honest, if you're going to be using Suse then stick with Suse (a headless Suse install is quite easy - it must be because I managed it and I am not that technical a sort of person). The openSuSE forums are well populated and extensive in their scope.
3) www.linuxquestions.org (http://www.linuxquestions.org) is a great place for highly technical help and probably has links to more educational resources.
Hope that helps some.