My first NAS, is this build good?

I'm planning to build my first NAS with UNRAID, but I'm wondering if the setup I have in mind is good or there is something I'm overlooking.
The goal is to use this NAS for:

• General storage (photos, documents, etc.)

• Backups (PCs, MacBooks, etc.)

• Torrenting (qBittorrent)

• Media center (Jellyfin)

• Self-hosted services (e.g. replacing Google Photos with Immich)

I'd like to use a Dell Optiplex 3000 Micro that I already owns with the following specs:

• Model: Dell OptiPlex 3000 (Small Form Factor)

• Processor: Intel Core i5-12500T (12th Gen)

  • 6 physical cores / 12 threads

  • Base clock: 2.0 GHz

• RAM:

  • 8 GB DDR4 Single-channel

• Storage:

  • 256 GB NVMe SSD (SK hynix BC711)

• USB:

  • 2x USB 3.2 SuperSpeed

• Graphics: Integrated Intel UHD Graphics 770

• Networking:

  • Ethernet: Realtek PCIe GbE Family Controller (1 Gbps)

  • Wi-Fi: MediaTek Wi-Fi 6 MT7921 Wireless LAN Card

The idea is to use the Dell as the processing unit and perform the following modifications:

• remove the NVMe SSD disk to free the M.2 slot

• use the M.2 slot to attach a SATA extender and plug the HDDs there

• keep the dell's chassis open in the rack

• use the internal SATA connector to add SSD for the cache layer

These are all the components I'm planning to buy and assemble:

BOX:
Extralink rack 19" 9U

FANS:
2x 120mm
1x Fan controller

HDDS:
5x WD RED PLUS 12TB
mounted with this HDD Cage
connected to the Dell on the M.2 slot with m.2 extender and m.2 to SATA card

SSD(cache):
1x Samsung 870 EVO SSD 500GB

PSU:
1x Cooler Master Silent Pro Hybrid 1300W (I know it is an overkill, but I already own it)

UPS:
1x EPYC NYTRO 800VA/480Watt



now, some questions:

1. Am I missing anything obvious (thermals, power delivery, airflow, etc.)?

2. Any reliability issues with running SATA drives off a M.2 to SATA controller long term?

3. Should I consider dual-fan intake (front or bottom) in addition to ceiling exhaust or heat will not be real problem?

4. Is the UPS strong enough to cleanly shut down the system in case of outage?

5. Any tips for improving performance or noise without increasing the cost much?

Any advice, warnings, or suggestions from more experienced builders are super welcome!

Thank you