1) Purchase a fairly, powerful old computer that has some extent of scalability as to its resources i.e. RAM, disk, processors, etc. I have a Dell Precision 7500.
2) Acquire a hypervisor (type I) of your choice: Hyper-V, XenServer, VSphere, KVM, or others. If you are going with a type II hypervisor, I would recomend Oracle VirtualBox.
3) It wouldn't hurt to have a NAS (Network Attached Storage). You can store your ISOs there. Mount them to your VMs (virtual machines).
4) Acquire ISOs of your choosing for installing operating systems to VMs. You can obtain copies of Windows Server 2012R2, Windows Server 2016, Ubuntu, Gentoo, or others online.
5) Basic network: WAP (Wireless Access Point), cable modem, and a switch with at least 8 ports and gigabit ethernet.
That should be a good primer. If you want ideas as to hardware to purchase, funding for virtual data center, certifications, just reach out to me.
Now that you have a virtual data center with a small; rudimentary network, you can build whatever you desire: databases, container servers, coding stations, proxy servers, virtual switches, et al.