structuring a hikashop site correctly

It depends. What do you want to do ?

It's better to have your products listing displayed in the main content area.
You can create one menu item of the type hikashop product listing for each category. Or you can have a module which displays a listing of categories which then brings up the products listing on the main content area.
That second option could be more difficult to setup and/or less customizable but then you don't need to add/remove menus when you want to add/remove categories in the future. If you think that you won't have to manage a lot your categories, the first option should be simpler.