I love that dock. I had four HDDs in two of these docks connected to one of my servers for a bit. Same experience. A bit slow for large transfers but fast enough for HD streaming. I think the space between the drives allows for enough natural airflow to keep them relatively cool. I think the hottest they got was 63 degrees Celsius during a large transfers. Usually stayed a bit below 60. In my janky homebrew NAS I see temperatures around 50, give or take 5 degrees. The use case should really determine the build so that may be the best option for many, especially with budget constraints.

The power supply probably won’t spin those drives and you may have some difficulty with thermal management. I used a SFF PC case with a SATA extender running outside to a few HDDs for a while. The drives got really hot until I got a fan running over them. This was a super janky setup though. Made a lot of dust. If you’re looking to stay low budget and don’t need RAID or SMART reporting then I would get an enclosure for those drives and just use USB. Otherwise see what you can Frankenstein from what you have. I built a NAS using my janky setup’s HDDs, CPU, and RAM. Got a cheap full size tower, old motherboard off eBay, basic cooler, and power supply for much cheaper than a new build. Still janky but upgradable with a lot of internal space for storage/GPUs.

What form factor is the m710q? I have a tiny FF so I’m imagining you trying to squeeze two HDDs into that… I was in a similar situation a while ago and broke down and bought a new case and transplanted my CPU and RAM. The options are only limited by your budget and needs when building

This right here. Since you can’t really configure the ISP router (1), DMZ is the way to go. The DMZ feature on home routers usually allows you to select a specific device or devices to add to the DMZ so make sure to reserve/set a static IP on your router (2) and configure the DMZ on your ISP router (1) to include only that specific IP. DMZ essentially forwards all ports to that device.