The default user is whatever you wish them to be.
As far as the listing and product view, editing the theme you can limit it to “is logged in” for the pricing. (this requires some heavy modification)
Once logged in, then the availability is there.
Magento has an importer that you can create custom profiles for.
You are able to associate column headers and import xls // csv.
personally, i like using Open Office with CSV utilizing double quotes to encapsulate and semi-colons as delimeters.
I am currently working on making a wholesale store of a multi-store cart.
We are using magento because its being designed as a full scale application (not a light script) to handle such things.
Good Luck in your decision process. It will take you a good hard month to get “intimate” with the product and all of its avenues if you are a developer, if not, longer.