Take a look at this post. I’m not saying you should do that exactly, but it might be helpful.
I would go with a more mature processor: Is that fine to run FreeBSD with AMD Ryzen 3 2200G? | The FreeBSD Forums
Is this ECC? It’s not a 100% requirement, but generally people build ZFS systems with ECC memory.
I’m a fan of mirrored boot devices, so I recommend getting 2. You could get away with a smaller one if that saves you anything. $27.99 isn’t bad though.
Last I checked, 8TB drives had the best price/capacity ratio. If you can, I would go with a mirror of 8TB drives and add an additional mirror whenever each time you hit 50% capacity. Not sure how much space you need starting out.
If you do need more performance in the future, 10GbE starts to make sense after you have a few mirrors.
Idk, that looks a little sketchy to me.
18" depth limit is pretty severe for a rack mount NAS. Sounds like the rack was intended for either network or audio equipment.
In general, you do pay a “rack tax” for rack mount chassis. I know your boss scored the rack, but if you have a place where something larger can go, that might be better.
Hope that helps.