Q: AirPort Express Set Up, Functionality, and Router Compatibility

I am considering purchasing AirPort Express but have some questions related to set up, functionality, and router compatibility. I have a Verizon MI424WR router in my basement, but I plan on setting up my Airport Express in the main level of my house so that I can connect it to speakers on that level. I want to be able to stream music from my Mac, iPhone, and iPad to these speakers through the Airport Express. Ideally I would like to also extend the range of the signal from my Verizon router (which pretty much *****) but the music streaming is more important. Essentially my questions are:

1) Do I need to connect Airport Express to an ethernet port when setting up?

2) Will it be compatible with (i.e., extend the range of) my Verizon router?

3) Do I need to do anything specific to connect Airport Express to my existing wireless network?

I'm something of a novice with technology so please dumb it down for me if you can. Thanks.