[seekingcharlie]

I lead design across a similar product (with iOS, Android & web). We have a web API & that's what our native apps pull their data from (we report on things like sales etc, so this ensures we're consistent across all platforms).

Re design - I'd literally do a design for each platform (iOS, Android, Web). There are huge differences between iOS & Android - they have completely different user experience/functionality so you can't just port 1 exact design across multiple platforms.

I'd highly recommend creating a UI style guide if you don't have one already. It's really quick for me to do 10+ screens as I'm using the same colors, fonts, etc in each file & then I generally just have to move blocks around for each platform.

Also, I recommend Sketch for design work. It's a lifesaver for designing between multiple platforms & everything is vector so it's scalable between different resolutions. A million times better than Photoshop for UI design.