I cant think of a single place to find all that information at once, but yes I can suggest a few:
1. Thwack -> Library & Support (first place to start with , you will find N-1 version details in here)
2. Thwack -> Links -> Click on the one you require , click on 'Learn More' on the product you require (you will find all new features here), click on Version History to check details wrt to previous versions.
3. Search for Release/Beta on Thwack
4. I am not sure what all modules are packed in a bundle as I work on standalone installs , to the best of my knowledge if you buy a suite of products together it would be packed in a bundle. You can just install the bundle at once on your primary and additional pollers. There wont be any need for you to worry about module upgrades separately in this case. Wrt upgrade on bundled version latest module versions will be packed in the bundle and when you upgrade the bundle all modules in it would automatically get upgraded to the latest version.
5. If you are using standalone upgrades , you would have separate bits for primary and additional poller (for a particular version), you install them accordingly on your pollers. There is a lot of information regarding standalone installation of application on thwack. What you will need to check apart from per-requisites would be the Compatibility matrix, when you are using the standalone method. You will find it on knowledgebase.
Hope it helps , you would definitely get lot many posts of this