Hi, To upgrade you just do a pacman -Syu. I started with 0.5 and am now running 0.6 thanks to that command.
As to gnome I have never used it but I suggest checking out packages on the front page of archlinux.org and it will give you a list of gnome packages. It might be something you would want to enquirer about on the actuall arch forums as their are probably more arch-users that use gnome there.