Are these same reporting capabilities also available in System Center Essentials?
No. System Center Essentials has built-in reports with the management packs, but data storage is fixed at 40 days. Also, there is no report authoring capability.
How about SQL 2005 SP2 and reporting services SP2?
SQL 2005 SP2 is officially supported for System Center Operations Manager 2007. DO NOT select the SharePoint integration option in setup for SQL 2005 SP2 as it will break SCOM’s Report Server setup.
What are the most common issues with IN-PLACE migrations from MOM 2005 (provided are pre-requisites are met)?
Check this article from TechNet magazine: Migrating from MOM to Operations Manager 2007 as well as this webcast ITPROMGT-203: System Center Operations Manager 2007 - Install and Management Pack Migration
You have two choice in migration, Side-by-side on the same hardware or side-by-side on new hardware. For in-depth discussion on migration download the MOM 2005 to Operations Manager 2007 Migration Guide.