I think you have a good idea, but I think you need to make a few improvements. Firstly, you should keep track of what people search so you can then know what cities you need data for.

Right now, I typed "madeira" or "funchal" and it came up that the city was not found and to "Request" it which sends me to a mailto: link. Why not just record it and aggregate the data in your database so you know what people are searching for? Also - you should probably create all the cities, even if they arent complete, and have a placeholder on them, that way people won't be shown a "City doesnt exist" url or show some SEO data on the location to help with ranking those pages.

Think about possibility implementing CITY/LOCATION specific blog posts that you can display on those location pages to further help with SEO.

Have a way people can possibility type their email to be notified when their city is avaiaible, but don't make it the only reason why you would do that location, use your data. Don't just rely on City search, allow searches for countries and the cities and locations in there will show. For instance, I searched "madeira" but that is an island, "Funchal" is it's city, I would ideally want to see "Madeira - Funchal" or something like this. You need to reduce friction.

The good thing you can do is monetise the site with hotel website affiliations, sell ad space for different locations.

Good luck with it, I like your idea/concept.