Is Spotify a bigger threat to Google's ambitions for music on Android or Apple's upcoming cloud-based music service?

I would say so. One big reason for Spotify's huge user growth success in Europe is because their lightweight, cross platform client software. If you compare that to Apple iTunes its definitely will be difficult for Apple to compete with that, unless they would release a iTunes "light", which most probably is not likely to happen. Another important factor is that Google Music will have hard time competing on the market, considering that both Apple and Spotify already have established several years of relationship with both artists and record labels all over the world. Content is king and one huge advantage that Spotify has against any competitor is that several of the worlds largest record companies actually owns a stake in Spotify Ltd.
You have forgotten about Amazon's Cloud Service. They recently opened up to allow unlimited songs as long as you have one of their higher services. I've tried Spotify and the only thing I could do is play the songs on my personal computer. If I wanted to do anything else, I would have to pay. You currently don't have to pay with Google Music. I had a $5 gift certificate for Amazon and so, didn't have to pay for it either. What does Spotify do that iTunes or these other services don't already do? I scrobble my tracks to Last.Fm via a plugin for iTunes. I don't need Spotify for that. For me, Spotify is late to the game and doesn't offer anything new. Nothing game-changing despite the long wait here in the U.S.
What are some good data science projects that can be done as a mini project?

There are many good project ideas listed here - A curated collection of interesting machine learning projects. They can be starting points.Pick a problem you really like to solve like a simple recommendation engine. Think about a few of your friends with interests similar to yours. Can you predict which books they would like to read, movies

How to start using Tesla Autopilot

Double-pull the smaller stick on the left side of the steering column.For what it's worth, this is a moderately popular question on the internet; many people have a hard time figuring out how to get going with Autopilot, in part because it's not start-able from the main driver display menus.

What are some of the most useful skills to know, anything from programming to parkour, social skills to dancing? What do you think is a skill you need in your life and that everyone will benefit from?

Useful Skills to improve your personalityStoicism - Be indifferent in state of pain and pleasure. Keep your mind calm in tough situations. Anger is a natural emotion, but we can master when to keep inside and when to put it out. It will save your reputation.