Try getting a used server. You can find one on labgopher. For the budget you have, don’t expect something great but it’ll be a start.

That makes sense. I’m a lazy guy and I didn’t want to try testing so I went with a known quantity.

You should take a look at getting sas enclosures. They’re pretty cheap, like $200 for a 16 bay. That will be so much more reliable.

Yes.

Here’s my advice. The most important things are that you have a free GPU slot and another PCIE slot on whatever you get. You’re going to want a GPU for transcoding when disk space gets tight. You want the extra PCIE slot for a sas card. Disk shelves are surprisingly cheap, and you can keep adding disk that way. They daisy chain.

As far as the OS, I’m partial to Unraid and Truenas but seriously, anything you are comfortable with will work.