You'll probably be disappointed with silk based off your concerns. Sure it's much lighter but wool is a staple for a reason.
Warmth: wool is far warmer than silk. Silk is pretty much only worn in hot environments (whether dry or humid) because it breathes so well. This breathability subsequently means it doesn't keep heat in like wool will. When wet wool will be warmer as well due to how the fibers work (water gets absorbed into the the actual hair fiber and not just trapped between fibers which keeps it warm while wet). Look at where wool and silk are obtained. Wool is from hair used to keep animals warm in a wide range of temperatures, but especially temperate to arctic conditions based off the species. Silk comes from cocoons of moths which are cold blooded and do not need the insulative value that wool provides.
Ember protection: I'm guessing here but wool usually has a tighter weave than silk. So even if silk smolders like wool does, because the fabric is so much lighter an ember will probably burn all the way through and then the exposed edges of the ember hole will begin to fray.
Odor: I've had a few silk shirts that I treated like regular cotton, having to wash regurlarly. Only wool and some special synthetics (Arc'Teryx's phase SL fabric) have been amazing at odor control.
Silk also chemically degrades when in contact with skin oils and sweat. It's a slow process but it won't last as long as wool.
I'm not trying to hate on silk by any means though. I live in AZ and wish I had far more silk shirts because they are amazing during the summer here. However if the weather is below 75F (where my desert rat self begins to shiver) I prefer wool because it regulates temps well. It breathes when I start to heat up from physical activity enough for 75F and yet will keep me warm down to freezing just by itself.
Hope that helps.
