Do not forget the UPS, or your backup system.
Copaxy Don't let this short sentence pass by unnoticed. At the end of the day this is more important than what hardware you use.
You sound unsure which direction to take. Save some money by buying some "learning" machines, so you can figure out what you eventually want/need. Pick up a couple of used towers on Ebay, Newegg, or something similar. Be careful to use reputable sources. You might even have some old 64 bit/dual core machines lying about collecting dust, or you might know someone who has this kind of paperweight taking up space in a closet who would love for you to get rid of it for them. Learn your way around OMV and its plugins/services/containers/dockers/etc. The money you save will allow you to buy a UPS and some backup disks and machines.