I wouldn't worry consider the environmental footprint in deciding my diet, but maybe that's just me. I read a book once (when I lived in a hippie communal house where people never used the heat, ate vegan, rode bikes, never flushed toilets to conserve water, etc.) and learned that it would have still taken 4 Earth-sized planets to support the world's population if everybody on the planet lived like me. If you live in an industrialized country then the vast majority of your carbon or environmental footprint is baked in: The streetlights, the roads, the infrastructure your taxes pay for, the fields that grow food whether you eat it or not, the cows that must be fed whether you eat them or not.
I think the lipids/fat relationship is not straightforward. For some I think a high fat diet does exacerbate high cholesterol levels, but for others, i think a high carb diet is the problem. For most people, diet has relatively little to do with cholesterol levels. (My husband has familial hypercholesterolemia and found that eating oatmeal, increasing fiber and upping fish intake helped, but a vegetarian diet on its own had little impact.)
On the flip-side, I think you have to take the case against sugar with a grain of salt (pun intended.) The evidence that sugar is not a superfood is ample; the evidence that it's a poison largely responsible for modern-day obesity is much more equivocal.