User Accounts

What's the best way to setup a sitefinity site to handle general public user accounts, estimated to be in excess of 75k accounts. The user accounts will be used to provide localization information such as weather, local news and also the ability to comment on blog posts. 

Just a bump for any input. 

What's the question, do you need to create the accounts?  Or are you just wondering how to set them up to store that weather\etc data?