Look at my ESXi system 1. It's almost the same MB (yours has an M.2 slot), slightly lesser of a CPU (yours is faster), and 64GB RAM (I have a lot of RAM). It's a fantastic setup. I use it to run ESXi and on ESXi I have a TrueNAS VM. I can run other VM's and do such as Linux, FreeBSD, Windows, or or I can run over versions of TrueNAS and link the hard drive pool to them just so I can test something new out if I want to. Or you could use less RAM, 32GB would be great if you are running TrueNAS on the bare metal machine. You could get away with 16GB but if you are serious about keeping this NAS for about 10 years, best to buy it now and be very happy.
As for the price of all three together. The motherboard alone is worth $300 USD new so all three together is definitely a good buy.
WARNING !!! It's used, will you have some sort of guarantee? 30 day month back? Or if it fails a test?
Run the burn in tests (RAM & CPU), and run them for several hours if not over night for each one. I'd recommend the RAM test for at least 24 hours, the CPU test for 5 hours but others will desire to run for 24 hours to saturate the CPU, CPU Socket, and near by components with the heat it could possibly generate. For myself, as a home user, no heavy long lasting loads, 5 hours works for me. I have done a 24 hour test as well, I just wanted to see what would happen. Well I still have the system so all passed. Just make sure you are allowed to test the system and if it fails, you can return it.
Does the CPU come with a Heat Sink & Fan? If it needs to be shipped to you, they need to support the heatsink & fan properly or damage can occur. If they pull off the heatsink & fan then you just need to reinstall it correctly or life will not be kind to you.
Lastly, you do not need an HBA at this point in time. You have 8 SATA ports, 1 for the boot SSD, 7 for hard drives. This will be fine for now.
So that should answer your immediate questions.
The only real concern I have for you is your use case and the fact that you want to expand it to 64TB of storage space and you don't seem to have a clear use case other than to run more jails/VM's in the future. I think you will likely change your mind on the storage capacity. Here is my general guidance on how to start out with selecting a storage capacity. How much storage space do you need right now? How much storage space do you think you will need in 3 years? Now double it. If you only need 5TB of storage now, in three years you will likely double that, now we are at 10TB, and then drives typically last 5+ years if you keep them cool and do not shut them down and spin them up a lot, so double again and we have 20TB. You could buy three 20TB drives and mirror them. Not sure I'd do that but it's possible. I would buy 4 drives that would add up to near 20TB.
Remember one thing, and it's important you understand this... The hard drives are consumable, meaning they will be replaced as they fail. They are the single most expensive component in the entire build. You need to plan on this happening. Generally the CPU/Motherboard/RAM will last the life of the system. You will have a fan or two to replace and those three components should last a long time, if you buy quality components. Don't forget to buy a good power supply. I have a fanless power supply (that is just my desire). I've been bitten before from a failed power supply fan. Fortunately the components you have listed are good quality. Hopefully they arrive at your house in good working order. And Test Them!
Hope this long posting helps you out.
