GON, with everything you post you have the skill to replace one of these springs. It's not bomb disposal or handling nuclear waste. Yes there's a lot of energy in the springs so you have to think about what you're doing and be deliberate. Yeah I'm one of those guys who hired it done once and said I can do that and when another spring broke I did and lived. I'll bet where most people get in trouble is not using the right tools to wind up the spring. I bought some steel rod the diameter of the holes in the adjuster cones and long enough to give good leverage, not a big screwdriver or whatever I could find in the toolbox. You can buy winding rods (I didn't know that). I think it's safest to have the cars out of the garage, if it would get away from you at least you don't damage a car. And it was mentioned about that torsion springs need to be lubed at least every 6 months.
Springs are rated by duty cycle, 10,000 or 20,000 etc so you can probably upgrade if you want.
All that said, having a garage door guy fix it is the smart money.
Using a table saw makes me more nervous than changing a spring did. Probably because dad cut off a finger on his.