Yes. Plugin includes Dynamic Load addon that will load rating blocks through AJAX. This addon is disabled by default, and if you use cache plugins, just enable this addon from plugin Settings -> Extensions panel.
Yes. GD Rating System supports import of rating data from:
- GD Star Rating
- WP PostRatings
- Yet Another Stars Rating
No. GD Rating System is completely new and different plugin, that has nothing in common with old GD Star Rating plugin.
Yes. Each site in the network can activate and use the plugin.