Active Directory was in Windows 2000, NT4 has a different domain technology. If you want to play with old Windows Server stuff, Windows 2000 would be a better, more coherent option, compatible with more modern software.
I ran a lot of Exchange 4.0 thru 5.5 on NT 4.0 and Exchange 2000 on Windows 2000 and 2003 back in the day. I can't say I miss any of that software (except, maybe, some faint happy remembrance of Windows Server 2003). Windows 2000 and newer are infinitely more useful and less quirky the prior NT versions (coherent OS servicing strategy, fewer reboots after settings changes, plug 'n play support).
I suppose there's an argument to be made for trying that stuff out to see why the newer stuff is better. In a homelab, though, you're never going to get to the scale to see why NT 4.0 domains were a pain point. Likewise, you probably won't be max'ing out an Exchange EDB size, or feeling the I/O pain that came w/ trying to sling content from a 50GB Exchange Information Store thru a 32-bit OS.
There definitely is an "ah, ha!" moment to be had looking first at the NT 4.0 Domain system, then at an Exchange Directory Service, and thinking "What if my Windows Domain could be like this?" (This was the genesis of Active Directory.)