Xander in Africa : It was in Angel's Damage episode. S5, Andrew shows up in LA, gives the skinny on where the Scooby gang is, although since Andrew isn't the most trustworthy of characters Xander might be anywhere else.

Hellmouth in Cleveland : It's one of Giles last lines on BTVS (if not the last), on Buffy ep. Chosen.

I'll go reread your latest 70 questions fics and give feedback. :)