Here are my answers :

But, how do I create and populate the initial set of tables that CI needs?

You can use any existing database you use for running limesurvey in its current form i..e v.1.91+ . Although some users have problems with using 1.91 database. So, i would suggest you to use 1.92 database. Installer for CI version of limesurvey will be integrated later on.

 What will the default admin password be?

Most probably , "admin" and "password" if you haven't changed it for the database you are using.

If you have any further questions, feel free to ask.

$hubham $achdeva

The best computer is a man, and it's the only one that can be mass-produced by unskilled labor.