Would melting sea ice lead to a rise in sea level? The ice is floating, so it's displacing the approximately same mass of water as it contains. If it melts the overall water level shouldn't change.
2. It's a feedback effect. Less ice means less light reflected means more energy in our oceans/atmosphere. In turn this creates more ice loss that won't be sea ice.
But like everything else (to various extents) it will expand when it's warmer.