puzzele Free game portals (low requirements): Clay.io, Itch.io, GameMix
You can also try Google Play Store ($25, one-time, non-recurring payment) I know you're looking for free publishing, but thought I'd put it out there since you mentioned the App Store.
I don't think Amazon will put ads on your game automatically (what if you don't want ads?), you'll have to use one of the various methods that are currently available - that tutorial should work and is the easiest way I know of.
Crosswalk (Android) doesn't support ads currently, and CocoonJS has a myriad of problems (and requires premium, IIRC).