Hey Hermann,
Sounds like you're already on the right track with regards to automation, and I agree with nielse, PowerCLI is definitely the way to go for that. Here's a discussion that I believe might help for the folder export/import:
Export/Import VM Folder Structure to new vCenter
As for the AD issue, I'd suggest if you're not already using AD groups (which in MOST cases would make it easy to transfer permissions) to use them. If you are already using them and it's still complex (I know I've seen a few environments that are this way) then PowerCLI may again be your friend. As for a guide on it, a guy compiled info from some discussions that took place here about permissions export and import here:
Unfortunately, as to your Flings question I don't think there's anything like that currently as far as I'm aware. Not a bad idea for a project request though, a backup/restore program for vCenter would be useful sometimes for time-saving. Thankfully it's all doable other ways, even if they are more work. =)
~Brandit