Hi:
Complex system, if the two websites you referenced are really what you are looking for. Not bad sites, by the way.
Will require a sophisticated back-end, for managing categories, specials, prices on actual products, artwork / picture upload for products (or do the products come from existing catalogs / sources?)
Payment gateways, shipment calculators, membership / login, customer feedback, related articles on a given product, related/similar products, etc. All of that and more will need specific attention, both front-end (users) and back-end (administrator(s)).
International shipping? Shipping methods? (FedEx, UPS, USPS, others?).
When a person returns an item, do you want to print a shipping label for them? Do you allow returns at all?
I work with PHP/MySQL on the back-end (server side) and JavaScript/jQuery, HTML5, CSS3 on the front-end (what gets downloaded to the visitor).
This is a big project, and we'll need some specs to agree on before actually getting started, so that we both know when the project is done (because, truthfully, this is the sort of website that is never "done," can always be expanded, extended, fiddled with, etc)
Looking forward to working with you,
Phil (Computer Whisperer)