Hi Nathan Pledger,
Thank you for your interest in Sitefinity v3. Yes, it is very different from and much better than the previous versions.
As to your questions:
1) In order to run Sitefinity in medium trust environment, you should do the steps described in Medium Trust Support topic on page 187 of the User Manual. As for the database migration, mentioned from you, it should work.
2) Actually, we are migrating RadControls to 'Prometheus' for in the upcoming Sitefinity 3.2. The current official version is not tested with 'Prometheus' controls. However, we can assure you that Sitefinity 'Prometheus' controls and RadControls will co-exist in the new release.
3) The RadEditor in Sitefinity is the same stand alone editor. Could you please give us more details about the XHTML compliance issues you have experienced with the RadEditor control?
4) Our goal is to release Sitefinity versions quarterly, about one month after the release of RadControls. Of course, Sitefinity will include the latest RadControls. Still, updating the RadControls at any time should not cause any problems.
Please let us know if you have other questions.
the Telerik team