Most of the Eye Winsome frame can be ordered as sunglasses. You can check this option under the description of each frame.
Photochromic lenses automatically gets darken when exposed to UV rays outdoor and turn back to clear when comes back to indoor.
If your sunglasses are non-prescription sunglasses then it will be thin but if your sunglasses are prescription sunglasses then it depends upon your prescription and lens index.
Yes , But with some specific frames you can get clip-ons.