So many questions...
Does he have an audience in mind?
Does he have any idea of how much he would sell them for?
(Calculate no. of hours on a sculpture, multiply by minimum wage -- would one of his sculptures be really expensive?)
If asked to do commission work, would he want to do it?
If someone asked him for a series of sculptures, or multiple versions of the same sculpture, could he do it?
Could he work to a tight deadline if required? (Sometimes, rapid success can be even more of a problem than relatively slow sales; does your uncle have access to other people who could help him if a lot of work arrives quickly?)
These are just some questions that came to mind quickly -- I'm sure there are many others. You can get web storefront software fairly cheaply these days, but you really ought to do some market research on this before you go jumping in. Could save a lot of problems later on!...