Hello Stephan,
I can truly understand the App gap issue that may users face. However, Microsoft is working on bringing the iOS apps to Windows OS. You can check for Project Islandwood for more information.
With regards to phone, currently they have the Lumia 950 XL (Flagship) and they recently launched Lumia 650 (Budget).
You can also check for HP Elite X3 that's going to launch later this year. This phone has Windows 10 OS and the specification are excellent.
Hopefully in near future they should be able to reduce the app gap because i personally like the Windows OS.
- Edwin