Profiles don’t hardly do anything to the bandwidth at all. You could have 10,000,000 users, and it wouldn’t make any difference.
Just standard hosting, with unlimited bandwidth, like bluehost or godaddy is just fine, nothing else is required.
If you really had 10,000,000 users, most likely, only 2,000 or more would actually considered to be “active”. So, buddypress is smart, if the user hasn’t logged on for over a year, the system removes the user from everything, but temporarily puts the account on “hold” if you would say, like a dormant account that isn’t using any space at all. It’s very unlikely that you have 10,000,000 active users, but it’s possible, and I still don’t see any issues.