the website wow.allakhazam.com has an addon called wowreader that (if you have an account, which is free) you can run it in the background and it will gather the data for each character that logs in and uploads it to their server. This gives you a page like this for each character that you upload. Cant track bank slots though.

Also an FYI, guild banks are viewable on the armory website as well if you login.