Noo, CP uses less resources, may be your explorer is onto something, try restarting explorer, explorer never uses that much CPU unless if there is something wrong..
Technically speaking, no. I log in with the Guest account and was in Metro UI. With my regular (admin) account, I killed Guest's Explorer.exe. Swtich back to the Guest session and the screen was black. So explorer.exe is also responsible for Metro UI screen.