the ebay stuff *should* be fine. kiln dried is dried, but it's always best to observe the wood for a few weeks in your climate to see what it does.
guitar wood is no different from other wood. my bass is being made from a piece of walnut i found at a lumberyard, and a piece of figured maple found in a pile of normal maple.
open grain just means that you will have to porefill when you finish, as the wood has visible pores.
the one being sold at touchstone is a special wood called "tonewood mahogany" that only grows in darkest africa, and there's only three trees of it known, but whenever it is cut down, another grows within a week.
there's probably no difference, except that the more expensive place costs more.
EDIT: the ebay stuff looks like one piece, which is generally more desirable than "two or three" pieces in the body blank.plus it's bigger