Erdogoat

It is always better to use 2 RAM-sticks, that way you get more performance because of the Dual Channel. But if you only have 2 ramslots it becomes more expensive to upgrade. When your motherboard has 4 Ramslots anyway just take 2 ram-sticks and you have enough room to upgrade. The RAM you picked is perfectly fine if you want to safe money but ryzen profits very well from higher ram speeds. if you can get that for cheap go for the higher speed

Btw there are some great tools for checking the state of your harddrive if you are concerned about it. Most manufacturers like WD or Seagate even offer their own ones.

Your symptoms do not match with a harddrive fail. If your harddrive oder memory fails you should normally get error messages. An instant shutdown really screams powersupply. I don't know how those games handle the savegames but you should lose all the data that is in your ram when the PC fails.

Anyone above 450W should actually do fine. Maybe you could explain how your PC crashes, do you get a bluescreen or does it just go black?

I would also try a different powersupply - it sounds like it can't handle the load anymore.