App with custom design and background images & available on Play Store/Apple Store

Hi, everyone

I would like to know your opinion about how to get a custom design, for example with background images. Is it possible? ( instead of changing the colours, I would like to create a more immersive experience with photos of my hotel, as background ).

Additionally, I am confirming what the best option is regarding the creation of an app that would be used by our hotel guests ( 25 rooms ). So, I assume it will have to be on Play Store & Apple Store, since paying 10€ for each user would be very expensive and difficult to scale.
What are the drawbacks of having the app on Play store / Apple Store? In termos of pricing, it would cost only 50€ per month per app, right? Are there any limitations of use? Is it easy to get the approval to publish on Apple Store?
I would appreciate your help, please :slight_smile:
Thank you!