If your hammer is delivering shock to your elbow you are using it wrong. And I don't believe that wood vs. metal makes any difference anyway.
Also, one drawback to jigsaws is that they don't cut straight lines. This is a benefit if you want a curve, but if you are trying to make a 2 foot cut in wood it will wander all over with a jigsaw. You can get a fence to help, but I think the goal is reducing tools not adding more.
You're spot on with your hammer comments. In my experience, people who have trouble with hammers are swinging from the elbow or wrist, rather than the shoulder. For optimal hammering, hold the handle as far down as you can, and put your index finger along the spine. It's satisfying to drive 12d nails!
Jigsaws are perfectly capable of doing straight lines. I remember helping my dad and uncle build a picnic table back in the 80s with little more than a heavy duty jigsaw, a sturdy work bench, and lots of 2x4s. Its a matter of making sure that whatever you're cutting is secured.
yes and no. The jigsaw I have has a little support wheel with a groove in it down near the work surface that helps support the blade. Also a certain amount of proficiency helps. The first time I used a jigsaw I found that it was real easy to unintentionally cause a bit of twisting in the blade. Using an edge guide helps a lot as well.
Also, one drawback to jigsaws is that they don't cut straight lines. This is a benefit if you want a curve, but if you are trying to make a 2 foot cut in wood it will wander all over with a jigsaw. You can get a fence to help, but I think the goal is reducing tools not adding more.
I personally would have both.