Migration from Windows to Linux

It looks like migrating a well-established business from Windows to Linux is an interesting project. Especially, if the business is not a stand alone coffee shop, but a corporation with 400+ users. Fortunately, prior experience with thin clients might suddenly get useful. Up to now I consider the following plan to be the easiest way (I am not a money guy, so, no focus on prices here):

1. Investigate alternatives for each and every application needed.
2. Configure small test environment with only few users (mainly from IT department) and run it for some time.
3. Migrate workstations of regular users.
4. Migrate servers.
5. Migrate development (New projects are done on new platform.Old projects are transfered gradually.).
6. Migrate workstations of “power” users.