for nas /homelab basically you require quad nic and maybe if you intend to do a nas build than some pcie to sata card and maybe multi NVME to pcie .If you want to make it a wireless router than an on motherboard m2 key and use open wrt
what could be a good canvas .My vote is on AM4 platform 1xxx to 5xxx series ( great upgrade potential) and DDR4 rams .Currently you will get used 1700 and 3600 which cost less and more cores more fun undervolt them use stock coolers and it will run beautifully. i was pretty much interested on those SFF machine but the scalability issue and it bespoke nature keeps me away from it.
Here is my personal experience:
For Storage: If you are just tinkering with stuff then you can get as many components as you need and have fun but honestly once you have had this hobby for quite some time and you consider the things you actually use (like if it goes down, you immediately have to fix it) all you need is a system you can add new HDDs into and a 2.5G port. Now if all you ever gonna have is say 20-30 TB of storage then any old (power efficient though) desktop will do but as your storage increases it's just a mess inside the desktop. Get an old server where it's just plug and play, I can't stress enough the QoL improvement that brings. Even if you stick to a desktop, get a RAID/HBA card which allows pass-through or JBOD like 9217-8i or similar cards; that 1x4 SAS to SATA breakout cable does wonders, cuz motherboard manufacturers add those sata ports in all sort of wrong orientation and places. Never buy a pci to sata card, not worth it.
Edit1:
For desktop, use whatever old desktop you have. If building new (I mean from scratch) Get one of those old school PC cases that have 8-10 hdd slots, they are cheap and awesome for this use case,
Platform: AM4 hands down (AM4 is still good for all kinds of things), buy used, get atleast ryzen 3xxx, wont cost you much more than a 2xxx.
RAM: cheapest green sticks you can find. Don't skimp on PSU cuz it has to run 24x7 nothing short of Tier 1.
Edit2:
For server: never underestimate the noise it makes and electricity it's gonna consume. The noise might make you go crazy. So as long as you got those two things figured out, a server is gonna serve you well. Also, try to buy it from someone who is in this business for quite sometime, in case you need parts for repair, you know who to call.
For compute and Network, as long as your VM host (desktop or server whatever makes less sound and uses less electricity..... go figure) can access the storage server you are good. That's why you need a switch, and no matter how much you want to save on a switch, you will be buying a managed switch 2-3 years down the line. Ask anyone with a homelab here, they have either already moved on to a manged switch or are considering to switch cuz it just brings those QoL improvements that makes life easier and makes having this hobby enjoyable.
Learn to wire your own ethernet patch cables, you will save time and money. I did my home security myself and god it was worth it to route cables the way I wanted.
Edit3 : Fixed Grammar