I considered buying a pair to make into clams, but my worry is that because of the stretch, they might "boing" upwards... I don't know how else to explain this, LOL... I just suspect they need the extra length to keep them in place. But if you do try it, let me know how it works! As for the weight, they are medium weight. They are not denim leggings - they are thicker than that. Average denim weight?
Can't remember what size I bought right now (and too lazy to go look). I recall trying two different sizes on in the store initially. The smaller size I couldn't even zip up, so that was a no-brainer. The next size up was a bit loose. I needed a belt to keep them from sliding off my hips. But after running them through the dryer - more than once - they shrunk into perfection.
They do stretch out as you wear them, but they don't bag in the rear or at the knees. They just get more comfy to wear. I can (and have) worn them as much as 5 times before washing again. I do toss these in the dryer - because of the price, TBH, I don't worry too much about it. They have faded slightly - not much at all.
The big caution I have with these is that they are very slim in the ankles and calves. I would not recommend these for anyone with wider calves/ankles, or large-for-their-size feet, as you could have trouble getting them on!
I suspect they'll look great on you, Yublocka!