That’s all possible with WordPress, and you have several choices. E.g. WP E-Commerce or Jigoshop etc
Scale-wise, it depends exactly what you’re wanting in terms of scale, initially and eventually. WordPress can be manipulated to scale quite far, you can buy a bigger server, shift a large chunk of your content and pages into the cloud, appropriate caching and server setup, and the right plugins, can go a long way.
Your biggest issue if you code your theme correctly and set everything up, will not be server horsepower, it’ll be network bandwidth, and that’s not unique to WordPress. The same issues will arise using Magento or Lemonstand etc