No matter what isbn you use, you keep all your rights. A createspace assigned isbn identifies createspace as your publisher; if you buy an isbn, you'll have to figure out a name for your publisher.
As far as selling, a createspace isbn limits your availability at big name stores like target or barnes and noble, but you'd have no problem selling copies yourself or trying out consignment deals with independent bookstores. For the most part, you'd be selling online. If you buy an isbn, you'll have to register your "publishing company" through your state (or wherever you may live) and possible pay taxes for it.
If your publishing for the first time, I'd recommend using the free isbn; you could alway republish it as time progresses! Don't make such a huge investment until you've really gotten the hang of self-publishing and you can afford it. 
(I've heard sometime people have trouble connecting their purchased isbns to their createspace accounts, so keep that in mind as well)