Welcome! Introduction to ZFS | TrueNAS Community and ZFS Storage Pool Layout | TrueNAS Community are a great way to start!
Be mindful to avoid SMR drives (ie WD Red); read Multiply your problems with SATA Port Multipliers and cheap SATA controllers | TrueNAS Community and What's all the noise about HBAs, and why can't I use a RAID controller? | TrueNAS Community in order to avoid common pitfalls.
You might get the question Is my Realtek ethernet really that bad? | TrueNAS Community and the answer is yes.
There is also the Hardware Recommendations Guide | TrueNAS Community, and the Terminology and Abbreviations Primer | TrueNAS Community might be of great help to reduce misunderstandings.
The bare minimum drives you need are a small SSD for the boot pool and two other drives (CMR if you are going to use HDDs) that will be mirrored (similar to RAID1).