If this is their first store, and they have no preexisting identity for their business, I think diving in with all that is a mistake. Test the waters with what they have to offer first, then if it goes somewhere.. they can do all that later.
Encourage them to try out yahoo stores, or amazon stores, or some other solution first.
I haven't used magento, so I don't have an opinion. But be aware that if it is open source, they will have to be ready to download updates to keep their software secure and up to date. Had a friend who was using open source software for a shopping cart. Their site was hacked. In the end, their FREE software ended up costing them A LOT of money.
Also, do they have a facebook fan site set up, or a blog? If they find those kinds of things challenging, then they will be overwhelmed with running a shopping cart.