Good summary and a lot of common sense - which we usually forget once we step on the floor of the gym.

Core work is probably the most important. I'm 69 y/o and have stenosis and scoliosis in my lumbar spine. My spine surgeon said that the core work I do is all that is separating me from fusion surgery. And the core is made up of roughly 30 muscles. If you can afford it, hire a trainer for a weekly or twice-weekly sessions.

As for working to fail - I do this mostly with my arms, chest, and back. Pick a weight such that you are able to reach fail between 5 and 30 reps. It works best for me to use a lighter weight and more reps. If I want to do pure strength, I increase the weight and simply do fewer reps.

Finally, use free weights rather than the machines. Machines isolate one muscle or muscle group. That's fine but in real life, when a muscle starts to fatigue, surrounding muscles kick in. Machines can't duplicate this. Free weights can.

Don't forget cardio. And have fun!