Hi Harshil,
You are correct in that it’s probably best to make versions for each device if you are looking to do something like a magazine in terms of design and layout with the bonus of everything digital should bring, interactivity, video and animation, audio etc.
The digital publishing tools were fairly good for delivering to mobile devices in terms of aesthetic freedom (using alternative layouts in InDesign) but now they are taboo from Adobe and replaced with the new solution (forgot what it’s called) that’s not cheap or a long term option to this conundrum based on previous support for digital publications in recent history.
It will be tricky to do a responsive design without a css and media query / flash like workflow in epub, pdf or as an app. Best would probably be to make it as web pages (and can live with those aesthetic constraints) but it’s no go if you intend to make revenue from it via purchase unless you have a market prepared to pay for pay walled content.
Best,
Sam