Excellent response. A few more points to consider for the original poster:
> I've recently been tasked with documenting our organization's IT infrastructure,
> primarily focusing on cost analysis of our hardware leases and software purchases.
You appear to have only done a -partial- cost-benefit analysis.
You state that you have a "marketing department ...composed...of Apple systems ...[using] Adobe Creative Suite", and need to continue to use Macs to support that, and a "Sales department ...[relying] on a proprietary sales platform that is Windows only"
Factor in needing the additional Apple hardware and software and the additional Windows licenses and other software. Factor in the support costs, patching, and additional IT expertise required. You may need -fewer- Windows support staff, but now you'll need some with cross-platform knowledge (Fedora and Windows),as well as dedicated Windows support staff and Fedora support staff.
Your Sales and Marketing ain't gonna move, unless you have credible replacements for the tools they are using and the solid support of a powerful majority of the corporate officers. They will bitch, and most of their bosses will shoot this up the chain. If they want to, they can and will derail -anything- you can do to bring this about.
Factor in the training costs, and the "I ain't gonna cooperate" costs. Look up "work to rule". Any of the staff who want to fight will do exactly as they are told, and call you for tech support if the reflection of the afternoon sunlight is causing a little glare.
I agree, -most- users could probably pick up Fedora quickly. But some will need a lot of hand-holding, and, of course, the Windows users will save documents in the newest Office formats, and they won't render properly in OpenOffice/LibreOffice.
And factor in your time. While you are doing this, you'll be taking time away from other work the company will want done.
If you convert, you're probably going to have to justify it in great detail, migrate slowly, and plan on much slower return on the investment.
And, as others have noted, while Outlook sucks, some people really do use the Calendar and scheduling features. There are some Linux alternatives, but you'll need to put a lot of effort into support to get started.
I agree, I'd much prefer Linux all around. But your organization doesn't sound remotely ready, and the reasons you're presenting don't seem compelling.
Licenses alone won't achieve the savings to justify this. You'll need a -lot- more return on the investment to do so.