Ask HN: I have an idea for a mobile game, but where do I start?

I have an idea for a web/mobile game, but I'm completely stuck on starting it. I'm an experienced software developer, but I've only worked on desktop and backend stuff so far, never got close to web or gaming or mobile in my career except for tweaking a thing or two here and there. It's a very simple puzzle game, but so many questions pop to my mind:

1) Should I use the DOM (like 2048 does) or canvas?

2) Should I use a framework like Phaser, Pixi, EaselJS, etc. for such a small game? If so, which one?

3) I want this to work both on the browser and as mobile apps. Is Apache Cordova what I need to use for this?

4) How do I deal with different screen resolutions? Every code sample I see uses hardcoded widths and heights.

As I said in the first paragraph, the game is very simple but I think (and the people I've told about the game agree) it has potential to be a good game. My initial thinking is to just use the DOM and go from there, but I have no idea if that's good practice.

I'm also not sure how to go about making other game screens (splash, difficulty and level selection, and the like). Can I just make those in HTML5 even for mobile platforms?

Any pointers are appreciated :)