You said you have C# skills so you might want to check out x42 coin. It's a new coin that seems to be made in .NET core technology using C#. The GUI wallet is made with Electron and Angular.
Also check out NBitcoin library that it is based on
https://github.com/MetacoSA/NBitcoinThere you will also find a link to the C# blockchain book
I mentioned above.