But some extra bucks wouldn't hurt, so how do I make some (coffee money) while making the App Open Source?
It's a feed reader, so not the next billion dollar idea
I'm willing to bet most people will rather pay small fee to have it installed from store and have automated updates than compiling it from the sources and running it themselves.
People who want to fiddle with the code or get the app for free can use the code and compile it themselves and people who value ease of use, can just one-click buy it.
I'd think more about other developers taking your code, slightly theming it differently, and selling it in the app store for a dollar less than you.
If you're ok with that, then go ahead. And no license in the world will help simply because you actually have to mount a legal challenge, and who's going to pay for that?
I'd say a better strategy to scratch your OSS itch is to make the underlying libraries OSS, but not the UI, that way you have some kind of value proposition you're offering.
It makes a little change every month and I've not had any complaints about the ads, except to offer a pay-to-remove option, which I mostly just haven't gotten around to yet.
You can also dual license it - for instance, put a public facing GPL version on Github and a private proprietary fork with proprietary extensions (such as advertising embeds) that you put on the App Store.