I'd perform your migration in test, first, to make sure you fully understand all the concepts. For example, this process will not move your SQL database from SQL 2005 to SQL 2008. Setup does not migrate the DB from SQL 2005 to SQL 2008, it migrates the DB from the 7.0 schema to the 7.1 schema. And you're perfectly fine to continue to use SQL 2005 if you like, though you can certainly move it to SQL 2008 if you want.
Are settings, jobs, policies, and packages migrated? Yes and no. Did you read the migration guide? It discusses what will change during the migration, and links to release notes that will explain manual migration steps. For example, if you modified Default policies for plug-ins, those policies will be reset to defaults. If you want to save the settings, clone them prior to migration. Policies will be disabled at migration time to ensure nothing is running and corrupting post-install.
Jobs and tasks will migrate for the most part, but again consult release notes. The same is true for settings -- most of these are in the CMDB and therefore migrate.
Regarding packages, most should migrate. But if you install the agent to a different drive on your new server (against the migration guide's recommendation), be prepared to manually migrate your patch packages or resynchronize on your new NS in the new directory. You'll also have to track down Pending packages or Retrying download packages and correct the paths to the correct drive. That's usually the case for patch packages and Plug-in packages. Finally, much, much data from deployment solution must be manually backed up -- though it should migrate, I did have to manually re-import some items.
Your site servers will need to be upgraded in batches. NS gets upgraded, then site server 1 of 12, then 1/12th of clients, then site server 2 of 12, then 1/12th of clients, and so forth. You do this so that an adequate number of 7.0 site servers remain to service your 7.0 clients.
There is very much you need to know to migrate successfully, and I'd recommend you read the ITMS Migration guide in full.