, as far as converting a raw OTA file to Odin files, here's what I can tell you. The OTA file should be filename.cfg, i.e. a cfg file. Believe it or not, this can be manipulated like an archive (like zip or rar or tar) so open that cfg file in 7zip, WinRar, or whatever. You're going to want to extract the files like (I can't guarantee this a full list, just the ones I can remember) modem.bin, NON-HLOS.bin, boot.img, recovery.img, aboot.mbn, rpm.mbn, sbl1.mbn, sbl2.mbn, sbl3.mbn (you might not have all 3, idk), and tz.mbn. Again, there may be others you need, and/or not all the ones I just listed might be necessary, they're just the ones I remember dealing with before. Oh, you're going to need to make sure the system, cache, and persdata partitions are all packed into .img.ext4 files, idk if they're like that in the OTA cfg archive.
Here's where it gets even hazier for me. So, I know from personal experience that you can take any of these files (I'll just use recovery.img for this example). In a linux terminal (I use Ubuntu for convenience's sake, my laptop has windows and ubuntu partitions) run this command:
tar -H ustar -c recovery.img > recovery.tar
So that's how you can take any one of those files I mentioned last paragraph and pack it into an Odin-flashable tar. I'm still a n00b when it comes to the linux terminal, so I can't really say the syntax for packing more than one at once.
So I guess I haven't really given you the complete process, but hopefully this is at least a decent starting point. Honestly I consider myself a hobbyist at best, not an expert. muniz_ri, who Devo7v mentioned earlier, did all the heavy work in this regard so he can probably help you much more, I just didn't want to volunteer him for the job