Comment All aspects considered!? (Score 1) 375
[time flow considered]
1] Focus on the cutbacks that don't require OS changes AFTER you made sure no actual OS change is required.
2] I think maintaining an inhomogeneous infrastructure with three different workstation OS is just overkill. Thus I recommend you to reduce that number (max. 2).
3] I strongly recommend you to migrate Applications first using the legacy system and then migrate the OS at once. Doing that way employees will notice slight changes over time regarding their applications (e.g. OO.org) and get used to the changes. When the OS change happens (e.g. Win -> G/L) they will notice the change in behavoiur, look, etc. but are ALREADY familiar with the applications!
4] Choose your GNU/Linux distribution wisely then. Fedora required you to dist-upgrade quite often. Is that ok for you? do you have the capacities to handle all the installations? Wil you use large portions of that distributions software (e.g. is there deamnd for SELinux/FLASK)?
5] Migrate the sales dept. machines to your target OS and the virtualize. It gives you more freedom, control and security (create VM once destroy often).
6] Avoid GMail. DON'T trust the organization begind (I didn't say company because it is none).
7] Adobe Stuff does not work so well using WINE. It depends on the versions of WINE and the target application softare however.