Ask HN: Introductory IoT development resources?

I'm interested in a few different IoT ideas and was looking for some basic resources for building things in that space. I have a physics PhD with a few years of DIY-style electronics experience in various labs and a good amount of scientific and web development programming experience. Some of my current questions are: 1. How to connect an IoT device to a mobile device through when on the same wifi. 2. How to connect when on a mobile network. 3. How should I approach hardware prototyping? (currently my sensor i think I need is just a camera. but possibly using something like a raspberry pi would be a good idea since it allows some flexiblity?) Any beginner/introductory material would be welcomed at this point, even if it doesn't directly address one of these questions. Thanks!