If you are not aware, Microsoft does offer evaluation versions of it’s operating systems and software like Exchange. This is great for those that want to learn more about Windows operating systems and software, but don’t have the funds for a MSDN or other licensing. These are 90-180 day evaluation versions (90 for Desktop OS’ and 180 for Server OS’), but if you are just getting started rebuilding a domain every couple months is good practice. RAM is cheap, build some virtual machines (VMs).
Microsoft’s Technet Evaluation Center – https://www.microsoft.com/en-us/evalcenter/
Prebuilt Developer VMs (Windows XP-10) – https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/
Alternatively for around $1200 for the first year you can pay for Visual Studio, which includes MSDN access to most Windows software and operating systems for testing purposes.