Good luck finding the tank. :) From the research I'd done, they appear decently hard to come by, unless you go through one of the European places.
As for tires, I've currently got some MT-21's w/ about 2k on there. They were pretty new when I picked up the bike, should have changed them out for something a little more street friendly. I've got a set of the Mefo Explorers waiting to go on sometime this spring. In the snow we got here, I couldn't get much traction. I've got a small hill on the side of my house and couldn't make it up the hill, had to try to get turned around and head back to the lower half of my yard. I think w/ some studs, they might do better, but I doubt I'll be finding that out anytime soon.