Apple Watch series 5

I'm thinking about getting an Apple Watch series 5, but I'm hoping that someone could clarify some stuff for me.For starters, what's the difference between a watch that cost $400 and one that cost $430? What's the difference between a regular Apple Watch series 5 and an apple Nike watch series 5? Lastly, what apps or features does the Apple Watch already come installed with and which ones would I have to download?

Those are all the questions I have for now and I would really appreciate it if someone could answer them for me or at least provide me with more information as to the ways I would benefit from getting one of these watches.