Out of all the words above, the one I am having the most issue is “Budget”

Not being entirely sure of what equals good server parts, I am even more unsure of what equals good second hand parts!

I bought a case ( https://www.silverstonetek.com/en/product/info/server-nas/RM23-502-MINI/ ) with the idea of buying second hand computers of Facebook marketplace to strip down and create something along the lines of an I7 based system. My lack of knowledge though means that I am unable to tell what motherboards fit… how many cores… what has sufficient RAM etc etc

Can you guys and girls help a bloke out, and share some links (based on Gold Coat Australia) with gear that may be appropriate to use?

Will mainly be used as a VM host, with NAS as secondary usage.

May build a 2nd one as a media server (currently have an old HP Proliant ML30 Gen 9 filling that role)

Current NAS are QNAP TA223 & HP microserver M36L