I would not go the route to setup a big Software (via the Motherboard) SSD Raid 1 to work on.
I bought a 12TB WD NAS (EX2 Ultra) for ~300€ and have it run in Raid 1. Next setup automatic backup once a week and you are save. A Synology NAS would give you better Software options and depending on the price more processing power (more options /usability) but it all depends on the price.
To save some money you could get yourself a DAS instead of a NAS. But i would at least get a 2 bay version that is capable of Raid 1 to get more reliability. And do not get cheap Consumer HDDs. You can get very good deals on (for example) Toshiba MG06ACA 6 TB HDDs that should run for a long long time and give you more bang for your buck.
Also depending on the finances there are way better options for fast storage (as your main working SSD).
Consumer SSDs do not have Power Loss Protection and do have a ~10x higher bit error ratio.
To save some money you could get a smaller Enterprice SSD paired with a Toshiba HDD and then setup Primochage. Gives you a fast and responsive system but a lot more storage space compared to a big expensive SSD.
All depending on price and what you want/need.
Hope you can get your most important Data back and (now some selfish thoughts) that you continue working on the project
If i can give any tips or help regarding Storage options please ask.