Siri will be a feature available only to iPhone 4S owners, hopefully Siri for iPad jailbreaks isn't too far behind. Not really sure why Apple is leaving this feature out of iOS 5 all together. iCloud will be made available for all Apple customers running iOS 5, along with OS X devices late next week.
You can go ahead an Download iOS 5 GM IPSW files since a UDID isn't necessary for the Goldmaster version. You do need iTunes beta 9 to install the iOS 5 GM on your computer. The GM is not available as an over-the-air update for users already on a previous iOS 5 beta.