Upgrading company's internal record keeping systems

See more:

C#

SQL

desktop

Xamarin

Excel-2016

The company I work for has grown a lot in the past few years. And so has their data. All of our accounts databases are Excel files used as databases for everything along with reports that are generated off of them. It has become increasingly difficult to introduce further metrics/KPIs/reports that need to be wiped off clean once in a while to make way for new data but this takes time due to size and complexity. In short, our current internal system for record keeping is no longer fit for scalability and maintainability. There isn't already a software out there that suits our current internal operations and so therefore a tailor made application is the only route forward.

I have some programming background albeit very limited but keen nonetheless. I know generally the direction I need to take to make a modern-looking desktop application that replaces at least the core of our current systems. This will go on to become a proposal to my company as a solution to our existing problem. Your help/suggestions on this rough direction that I am taking will be really appreciated.

The criteria for my approach to selecting the right technology in order to create this application is based on the following:
1) This technology/programming language I learn to make the application has to be applicable and relevant to current times but will also hold value in future.
2) All the computers running in our office are based on Windows Operating System.
3) (Optional) The very same technology/programming language could be used to build a mobile application that is a mini version of this said desktop application re-using the code that is used to build desktop software.
4) My primary and secondary IDE will be Visual Studio and Jetbrains Rider respectively.
5) This technology/language must have strong community support with plenty of libraries.
6) Because our current system is all based on Excel, the technology should have strong support/links/libraries to work with data from Excel files.
7) Integrated support for modern-looking UI/UX.

The direction that I think I should be taking based on the above criteria:
1) C# for business logic/main technology/Xamarin.
2) WPF for User Interface (XAML based).
3) SQL based Relational Database (not sure which database technology I should be using but it will need to work flawlessly with VS, compatible with desktop and mobile applications (Xamarin).

I will have invested a lot of my personal time to create this proposal so it is extremely important that I take my time to plan this direction earlier on and that is why I am seeking your help on this.

Any input will be much appreciated.
Thank You.

What I have tried:

Research into different technologies