I'm not sure if there are any visa experts on here, but for what it's worth, I believe that your visa is issued by the country where you will first enter the Schengen Area. And so it's their policies that you need to research.

You can make fully refundable ‘pay on arrival' reservations for all 30 nights, if necessary, and so fulfill that requirement. (Make sure to cancel them later!). But I would think most border guards understand the idea that not everybody has a set itinerary.

For what it's worth as a Brit - so no visa needed, but various restrictions on me now - I've only been asked to show proof of accommodation once in half a dozen entries to Schengen. That was at Zurich airport.

I was quizzed at Helsinki airport when I told them I didn't have a set itinerary beyond the first couple of nights, or even a ticket home. But it only took a couple of minutes and he let me in.

Thank you ralderton