you want to be super careful when "cleaning" the exterior of a meerschaum.. the stone is porous, and very soft.. any abrasive material will scratch the surfaces pretty quickly..
also.. many meer owners like their pipes to show age (to include staining)...
because meers are porous, they will pick up oils from the hand, which will over time begin to discolor the pipe.. they also change color over time/use from the heat in the bowl...
old, well used meers will turn shades of yellow, brown, pink, etc.. just from handling and use.. which is considered highly desirable by some smokers..
If you absolutely must clean the exterior, I'd recommend just warm, soapy water, and a very soft cloth... and cotton swabs for the crevices..
Another good thing about meers.. is the inside needs much less maintenance/attention than wood pipes like briars.. they do not build up a "cake" like wood pipes do.. or have some of the other common problems..
IMO for the inside, all I would do is run a couple of soapy pipe cleaners through it.. followed by several dry ones.. and then fire it up... it doesnt look like its ever been used before.. So I dont think it will need much more than that..