Maybe we should start from the beginning.
ECC is RAM related. It's Error Checking and Correction. It makes sure that the values stored in RAM are checked. The values in RAM are what is taken whilst files transfer through the CPU, and thus if these values change while writing you can corrupt data. Because modern CPUs have integrated the memory controller onto the CPU, you need to select a CPU which supports ECC, RAM that is ECC, and be willing to pay for it. It costs more, generally is slower, but is the way to go when money is no object. If all you are storing is media, then you're likely not going to need the expense.
RAID is how you hook up a hard drive array. Here's the short of it. You need to choose what type of RAID array you want. There are a bunch of types, which all have their ups and downs. Here's the real issue, adding a new drive every month, as funds become available, isn't really supported (in anything but JBOD). If I build a RAID 5 array with 4 disks, and want to add a 5th, I have to create a new array. That means exporting all data somewhere, destroying the old array, building a new one, and then importing the data back. This isn't going to be a 20 minute drive pop-in and bootup.
As far as selecting RAID, you're going to have to figure that out yourself. The common types are:
0 - Striping - Data is striped to drives. This is fastest, but any failure borks all data. - 2 disk minimum
1 - Mirroring - Data is written to each drive. This is very costly on storage, because you functionally lose half of your storage space. - 2 disk minimum, must be even number of disks
5 - Stripe+Parity - One drive can be lost, and recreated. You lose the storage of 1 drive. - 3 disk minimum
6 - Stripe+double parity - Two drives can be lost and recreated. You lose the storage of 1 drive. - 4 disk minimum
What you don't see is that all drives must be the same size. If they aren't, then best case is you have whatever is the smallest drive. Additionally, rebuilding arrays is a royal pain. My 12 TB array (16 actual, RAID 5) took nearly a day to rebuild. That was with a dedicated RAID card, not the Intel rebuild (tried it back in the SATA 2 days with a 6 TB build, and it took more than 2 days).
So, maybe you need to evaluate a few things. Is absolute security a concern, because if it is your budget is not in the right area code. Is your goal a media server, that might better be served as one of the available NAS solutions on the market? Maybe this is all still a little bit new, and you should do some reading and decide on something a bit more permanent.
I'd suggest that a NAS that can do what you are looking for is in the $2419 range on Newegg right now.
https://www.newegg.com/Product/Prod...TMATCH&Description=nas&ignorear=0&N=100158125 601286743 601299072 601299171 601299369 600418376&isNodeId=1
Your budget is less than a third of that. You'll have to learn about Linux, or buy an OS. You'll have to figure out how to share over your network. This isn't exactly something you slap together in an hour and start flying with. I think an evaluation of priorities, and skills is in order. From personal experience, Linux is a mess the first time a person tries to get it working. A NAS wraps everything up in a bow. By the time you buy everything, get the cards, the OS, etc... you'll probably spiral up to the $2000 mark. You pay an extra $420 for a real warranty, developing software, and convenience. In my experience, that is worth is when you want something that just works.
