I am currently having to plan out a similar organizational split....
Right now, my plan is to create cloned suite(s) (QA, Staging and Prod) (using the same tracking configuration) - I am going to see if Client Care can create a copy of the Prod suite with data (so that whoever gets moved will still have access to their historical data, but it may just be a "so sorry, I can't do anything" situation).
Whichever of the above happens, I then plan to copy my Launch properties with all the rules and extensions....
Then on the new Launch Properties, I will change the suite references and configurations that need to be done, and have the site(s) going to the new properties first make the Launch script change in QA and run through a full test cycle and make sure that the tracking all still works.
Before going live, I will also go into the Admin Panel and create new user groups (luckily, I set up all access via groups, rather than adding all individual suites to each user) so I will then give a grace period where the users being moved have access to both system.
I will also need to replicate critical reports to use the new suite, and update my Report Builder Reports to match. I will also need to set up new Raw Data feeds for the new suites.
Once I have everything, or I think everything, I will have the changes made in prod, keeping an eye on the data for a while... then when we've had enough grace period, I will go back in and remove the original user group from those users, effectively shifting their access.
At this time, I am not planning on setting up separate "companies" within the organization... but this can be done too... but that would make my job much more difficult having to switch between them all day long... but IF you need to do that, you can. Adobe Client Care can create new companies within your organization, and IF you have some suites that aren't globalized, and need to be moved over, they can change the references for you (I did the reverse of that, migrating suites from multiple companies into one about 5 years ago....)
