Answering another Question, I pointed to this tutorial:
Creating a Simple Backup/Restore Settings Feature
Lee Pham on Jun 22nd 2012
In this tutorial, I’m going to show you how to create a simple backup/restore feature for your WordPress blog. With this feature, you can backup all options to another place, that you can restore them from at any time without configuring them again.
All Widgets options are stored in wp_options table.
So, the plugin developed in the tutorial will deal exactly with the information not handled by WordPress Exporter/Importer, i.e., restore all Widgets and all other site options.
I haven’t tested the plugin as it is intended nor in a MS environment. I used it to create a plugin import/export options page.
If you want to run something just after a site creation, check this Q&A: Redirect to a Plugin Settings Page After Multisite Site Creation?
IMO, the second Question, “How to Auto-Import a XML?”, deserves another Q.
[update]
It is possible to modify the default content for new sites (Hello World, Uncategorized, Sample Page, Blogroll) using this technique: Populate content on install