I had a few alternate answers to a couple of questions:
You're mostly correct. By default using your exact examples, your default web directories would be:
Your mysql hostnames can be any subdomain that you create. You create a subdomain specifically for mysql use and it can be whatever you want as long as it's either a dreamhosters subdomain or a subdomain of a domain you control.
Downloads through http are only limited by apache limits on filesize. That said, our download speeds aren't blazing, but are respectable. Search this forum and you'll find examples of download speeds that various people are getting.
Don't forget to look around here for some good upload scripts like uber-uploader. There is a limit on the filesize that we can upload using php and uber-uploader seems to be the most highly recommended alternative.
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They're Dreamhost coupons!