No NAS needs 32GB. Ever. Not even FreeNAS, despite what the neckbeards say.
Just go buy a Synology DS218j or similar. Your knowledge level is limited at best, you're not going to be able to build your own. Suggesting 32GB of RAM for a 6TB NAS shows that lack of knowledge.
This.
I bought an HP Microserver must be five years ago and it's been running FreeNAS since. 4TB originally, now 12TB of storage and 8GB RAM is enough. I've had to replace a failed disk, but that's about it. Needs very little processing power - this one runs a dual core AMD chip intended for laptops.
You'll find a Microserver used for not a lot of money if you fancy something less off the peg than a Synology and far cheaper than an overspecified server.
Data is accessed over a network share. Windows (or Mac or whatever) doesn't care if the data is stored as ZFS on the server, it's just sees a CIFS network share.