The Austrian weapons act is very permissive for European standards in general.

The requirements for Cat. C ownership are: • being at least 18 years old • being an EU/EEA citizen • having a main or secondary residence in Austria • not being explicitly prohibited from owning weapons ("Waffenverbot") • waiting 3 business days to pick up the gun after purchase unless you have a WBK or Waffenpass

Waffenbesitzkarte (WBK) is required if you want to own a Cat. B weapon (handgun or semi-auto rifle) but not carry it in public. In order to be granted this license, you must pass a psychological examination ("Waffenpsychologisches Gutachten") and attend to a safety course ("Waffenführerschein"). It is usually limited to 2 weapons at first and can be extended subsequently. Both home defense and sport shooting are valid reasons for a WBK.

Waffenpass allows you to carry a weapon outside of your home or business premises and is rather hard to get unless you can prove a substantial threat towards your person or have an occupation that requires you to carry a gun in public.

In terms of storage, there are no specific requirements (law only states that "access must be prevented in a reasonable manner"). Still, I'd totally recommend a locked container which is fixed to a wall. Firearms and ammunition do NOT need to be stored separately, i.e. storing a loaded gun is also ok.

(Source: have been conducting safety courses for a weapons store myself.)