Then I came back to this site and saw the pro version...

Here's the deal: I'm trying to set up a website for my sister's business, and she knows zilch about anything to do with computers so I'll be teaching her from scratch. The pro version looks like it does so much more and to me it seems easier to navigate, but I've fiddled with other websites and setups that had admin areas. So I was wondering how folks felt who were new to this whole type of experience and if they liked the pro version better.
I'm half expecting the whole online ordering thing to never get fully used by her, so that brings me to a few other questions: If I purchase the pro package, is it transferable from one site to another? I currently have one online store and will be opening another website for book-selling. I'm guessing the pro package is just for one site, so if I use it on 2 different sites do I have to purchase 2 licenses? If hers never gets used can I just close it down and use the same license on another site?
And with both the free and pro versions: is there a limit on the inventory? My sister's store is no big deal, maybe 20-50 items. But if I use Agora on my upcoming bookstore I'm looking at one time sale items (old books) with an inventory of probably 10,000+ books.