This question comes by quite regularly. Generally there are two camps:
1) of course you can do it with one system, take a relatively fast CPU on a platform that lets you clock way way down and you can do everything from 1981-2000 on the same system.
2) no way, the compromises you need to make to shoehorn it all into one system are far too great, give yourself a break and break it up into multiple systems.
There's truth in both approaches, what determines what is best for you is mainly whether you're purely in it for the software, or whether you also want period correct video and (particularly) sound hardware. If software, there's no real reason not to go with option 1. If hardware, option 1 is really, really tricky/frustrating and option 2 is far more attractive.
I'm a hardware person, I even have two almost identical late 486-era systems simply because I want PCI in the one and VLB in the other, and have more sound cards from that era than you can sensibly fit into a single system. Tbh I spend a lot more time acquiring, testing, repairing and installing hardware than I actually do using it to play stuff. A single system would NOT work for me. But that's me, you need to decide for yourself.