Like other people have said, it’s going to depend on what you want to do with the NAS. If it’s going to be a pure NAS (ie network storage only), then using onboard will be fine. If you plan on doing other things (home assistant, media server, etc), I recommend going the virtual machine + HBA route.

I used a hodge-podge of chinesium parts and leftover drives to create a DAS system that hooks up to an HBA via DAC. I’m actually kinda surprised how stable it’s all been.