I played around with phonegap before, trying to make use of the native camera through the phonegap api, but never finished it. I found it cumberstone/slow to debug, but everthing else, is just like developing webapps. This time, it really was developing a web app. I used chrome (and chrome developer tools, with the ember debug plugin) to develop the app until it was completely done. Using the phonegap cli to build out an ios, android and firefox version took just a couple of hours, and the phonegap documentation is very helpful. So overall I would say, if you are not using phonegap's native api, and all you need is a wrapper for your html/js app, go for it, it is super simple...
Really appreciate the quick response, and good luck on this endeavor.. as someone who's passionate about fitness I can appreciate what you're trying to do.
For ember I feel like the official guides[0] are a good place to start. I found that a lot of other guides or blog posts where heavily out of date, since ember has changed quite a lot in the last couple of months. There are two other guides that I skipped over, which seemed to be pretty good [1][2].
For phonegap I always just used the official docs[3] and stackoverflow for times when i was stuck. There is one thing i can highly recommend though: Install the webview-debug plugin[4] for phonegap. With that you can make use of the awesome remote debugging functionality on android.[5]
And one more resource I can highly recommend is brunch.io[6]! It is a tool to help you structure your html/js app, it bundles all your files together, compresses them and spits out 3 files in the end: index.html, app.js and vendor.js. And that's the 3 files you put into your phonegap folder. You can even setup brunch.io to automatically push those files into your phonegap folder everytime you change something. This is not ember specific either. There are nice sceletons to get you started with backbone, spine, angular, etc..