|Re #7 & 8.|
It would be as well to see if the temperature rises when the computer gets used and particularly if you can catch the readings just before it crashes. We need to eliminate overheating from the equation.
There is one very simple thing I have sometimes run into and that is trouble with RAM edge connectors. A slight vibration can move them onto an oxidized surface. Clean their edge connectors with a pencil eraser and pop the sticks in and out a few times to clear any oxide off the sockets themselves. While you're at it do the same for any circuit cards and also ensure all the plugs and sockets are firmly home. Apart from overheating, it is tricky with this fault to even decide whether it is a hardware or software issue.
Have you run your Anti-Virus lately? It seems a long shot for this one but it would do no harm run MalwareBytes freebie on it just to make sure there is nothing bad around. It's a good little program that often finds and fixes what AV's miss.
We all live on a ball.