Think Machine, I think you're overthinking it.... Seriously though
1. all of the "blue zone" areas that are the longest lived people on the planet follow diets based primarily around starches, legumes, fruits and vegetables which are inherently high carb diets. The china study, John McDougall, Caldwell Esselsytne and most other lifestyle treatment physicians utilize high carb diets for their patients. Their programs may not be necessary to follow to the "T" for a healthy person, but I think its same to say that they are not going to harm your health.
2. I've wondered about excess weight in the form of muscle decreasing your over all lifespan as well. But my dietetics professors have unanimously said that is not the case. Of course, they could be wrong. But I will say that it seems unlikely that without the assistance of drugs you are going to gain the extreme amounts of muscle that it would take to put enough stress on your heart to decrease your over all quality or life span too any measurable amount. And if you do, then Caldwell Esselstyne whom I quoted in "1" has written a great book based on a highly effective program called "Reversing Heart Disease" in which he puts patients on a low fat whole foods vegan diet and they get better.
3. If you lift weights you could potentially get an injury, that's true. But if you don't lift then your chances of osteoporosis (mostly for women, but men too), sarcopenia (muscle wasting/atrophy), hip fractures in old age, and even cancer increases. So make practical incremental increases in your training and not crazy psychotic jumps that you're body can't handle and your chances of getting injured will greatly decrease. Learn how to squat with lighter weights and you will find that the squat is used more in daily life than probably any other motion apart from walking (and possibly using a remote depending on if you are a gamer).