Processors and RAM
You should probably have a look at the Dell T340 or T350 servers. Make sure to get lots of processing power and lots of RAM. Something like the Intel® Xeon® E-2386G 3.5GHz, 12M Cache, 6C/12T, Turbo (95W), 3200 MT/s might be a good processing choice. At the time or writing I would go with 32GB of RAM.
HDD or SSD? The question isn’t as easily answered. Server SSD are super expensive. Desktop grade SSD are not. You have a few options the way I see it if you don’t want to spend the thousands or server grade SSDs.
You can simply get a server grade SATA HDD such as something like a 4TB Hard Drive SATA 6Gbps 7.2K 512n 3.5in Hot-Plug, and be done with it. No adding extra drives. The downside would be that you might not get the transfer speeds you want. Of course there are other variables like having the correct USB cables and having the proper ethernet cables that transport your video and photos to the HDD. This single HDD setup is probably the easiest to setup and the cheapest to buy.
Other option would be to get the smallest server grade SSD you can get (least expensive) and then add 1 or more extra desktop grade SSDs to hold your video and photo files. You would run the operating system from the server grade SSD and then mount the desktop grade SSD(s) to your storage location. With this type of setup you would get the durability/reliability of server grade hardware, except for your storage drive. You can go with multiple 1TB SSD and create a RAID drive or you could just go with one large SSD. I used four 1TB Crucial SSDs in a RAID 5 array at my DZ and they have lasted 2 seasons. The downside of using desktop grade drives is that they may not be as durable. However, your storage drive is only a temporary location for customer media. Once customer media has been uploaded to a cloud location it is not required to be on the storage drive any longer. You could also have a backup USB SSD that would be ready for use in the event that your desktop grade primary drives failed in the middle of a jump day.
With regard to the extra desktop grade SSDs you would need to get an after market (or OEM) drive bay(s) for your Dell server with a 2.5 inch conversion kit to install it. Alternatively, you could go with one 2TB portable SSD and just plug it into a USB port on your server without having to deal with setting up a drive bay. However, I have not tested this type of application and am unsure of how it would perform speed-wise.
Running Vidiot server on a Mac Apple computer
Certainly possible with XAMPP installed. However, Mac computers are generally more expensive than PCs with the similar hardware components. It’s not really economical to buy Macs to run your video program. On the other hand, if you already have one (or two or three) go ahead and use it. You can also use Macs as dropping stations, too. You can even mix and match PCs and Macs and run them with Vidiot. The key is just having one super computer as your Vidiot ‘server’.