ID or OD?  

As for the header tape, 1" wrap would be easier to work around the curves than the standard 2" but the two inch would work better on the straight portions of the pipe.  Order it online.  You can get a better variety and colors for a lower price than any store I've seen.  You might consider getting the kind with ceramic coating that won't flame up should you get some oil on it while riding.  It's about 2-2.5 times the price of common fiberglass wrap though.  

The only wrap I'm using right now are two strips, one underneath each clamp for my heat shield.  I ordered black fiberglass.  Those two little pieces have turned tan already.