Thank you, caitlyn, for your reply! I have testing repo enabled, though I don't do upgrades just install new stuff.
The thing is - I've read somewhere on the forums that Gnome is included in VL5.8 repo. To be honest I was quite surprised - I've used Slackware from 10.0 version and had quite bad experience with Gnome (including Dropline, Freerock, except GSB). That is why I checked a little bit 5.8 repo and got curious about how stuff works.
So I got answer on questions no. 2, 3 and 4.