dashboardgesturelaunchpadtrackpad
I don't really have a use for Launchpad, but the gesture to me makes sense for Dashboard. I experimented a little with BetterTouchTool, but it doesn't have the gesture available, and I'm not sure it would work well with the sequence of successive pinches and spreads to go from desktop Expose to overlay (normally Launchpad).
Ideally I'd like to see if there's a plist tweak that can be made somewhere that would keep the gesture behavior exactly the same, but substitute Dashboard for Launchpad.
To summarize...
As in iOS, you can organize your Launchpad icons as you please using drag-and-drop. You can reorder apps, move them from one page to another, and even put them in iOS-like folders. Note that Launchpad folders are entirely independent from the /Applications hierarchy: creating a folder in Launchpad won't create a folder in /Applications, for example.
Your problem seems to be related to the fact that you've got so many apps. Again like iOS, there seems to be a maximum on the number of pages of apps Launchpad can handle. If you really need all 400+ apps on your Launchpad, there's not much you can do other than reorganize everything into folders to free up some slots. But I doubt you need instant access to everything Adobe has ever installed on your computer, so you have a few more options to clean out your Launchpad:
If you just want a clean Launchpad, option three is probably your best and easiest answer. Options one and two are there if you like to keep your /Applications folder clean, too: useless apps might as well be deleted, and your CS4 uninstallers could probably be moved somewhere a little more out of the way until you need them.
Finally, you hint at having problems with having Launchpad duplicates. As I mentioned in an answer to this question, this may be a problem of actually having more than one copy of the same app installed.
Hope this helps clear up some of your upgrade troubles!
Best Answer
I'm not sure if there's a plist modification you can do to alter the behaviour, but I do know that BetterTouchTool will let you replace the pinch zoom in/out gestures with custom actions. You can assign them to activate Dashboard instead of LaunchPad if you like or any number of other things. It can be a bit involved to set up, but it is very powerful in what it lets you override from the OS X defaults.
TUAW has an article on customizing a Magic TrackPad using Better Touch Tool that demystifies it a bit.