You can use a Bluesound Vault as a NAS, but they are terribly slow and imo not really fit for purpose. The easiest way to find the address to your devices should be using your routers DHCP table, where it displays it’s leases.
Your Vault also shows its ip address through the Diagnostics-page, second from bottom of their menu.
You don’t need to add a username or password and your Vaults addrsss would most likely be something in the vein of:
\\192.168.1.35\share
But you need to check your particular settings.
Where is your Roon Core located? You will be a happier user of Roon should you decide to copy your Vault library contents to a local drive connected to the Roon Core (USB or Internal)