As quickly as possible is expensive and can lead to making choices that cost a bomb for very limited perf gains with your use case. As fast as possible is probably a pure NVME + SSD setup with more RAM than you can shake a stick at and some 40gbps NICs
I think I'd be looking for 32GB minimum to start with and at least 8 decent enterprise type HDD's. I would only increase the RAM if needed - I wouldn't bother with a read cache, and get the biggest drives you can get your hands on as well (as long as not SMR).
I would give the TrueNAS/Freenas forum/wiki a decent search if you looking to do a modern AMD build as I think Freenas can be quite picky about what it will run on compared to Linux based systems (E.G the cheaper 10G Aquantia NICs don't work well if at all without some decent FreeBSD knowledge - and even then you will find you break the driver doing OS updates).