HBAs are essentially just higher performing sata ports than the stock Intel, AMD, or Marvell chipset sata ports. Useful if you need the fastest performance from your spinning rust and sata6 SSD drives and larger NVMe configs aren't in the budget. For a home NAS, which tends to have very limited writes (media storage) and few concurrent connections, the onboard sata ports are still just fine.
You may or may not need to use software raid with a HBA. You can always just access each disk individually off of it (like Unraid wants to do). Or use an OS-controlled software raid like LVM, mdadm, or ZFS. These will be much more robust solutions than the fake-raid provided on cheap raid cards with respect to error and failure recovery. Finally, current best practice is to use mirrors (and take the 50% capacity hit) for ease of expansion, rebuild times, and throughput over single and even double parity configs.