It would be great to have an installation wizard. On the first run, the user could be asked for:

• The main extension points: type of credentials provider, users and groups manager, and so on.
• Main database server type
• Main configuration information depending on the information previously provided
• Select or create an administrator user, depending on the users manager
• Main site type, title, languages and skin.
• [...]

After all this information gathering, initialize the runtime.xml, config.xml and database.