I apologize for the delayed response to your other questions.
1) Mysql connections are 30, 2) A single IP can connect to a site up to 20 times concurrently, and an FTP/shell user maxes out at 10 concurrent connections, which can also be killed off from Users > Manage Users > "Kill FTP Connections" in the web panel.
We do have a cPanel importer that we've built to help migrate your sites to us from any web host that uses cPanel. Please see for more information: http://wiki.dreamhost.com/CPanel_Importer
If you have trouble with our cPanel importer you can reach support directly with details. Alternatively, you can follow these to transfer your sites manually:
Let me know if you have any other questions