Hi Jun, welcome to Meta 
For the first question, that is the Solved plugin. Look for empty box on unsolved in site settings and uncheck the setting.
Not sure about the rest of your questions as I don’t use the fakebook theme. What device are you using?
There are topics in the Theme component category which may interest you for example Discourse Bars 🍻 🍸 (a sidebar framework) if you’re looking for places to place stuff around the page.