You will find that the transition from Java to C# is pretty smooth. Working with .NET has become much more intuitive and has a lot to offer. I highly recommend using Visual Studio as your IDE. It makes things much easier and is not too different than other IDEs like IntelliJ. There are also Visual Studio templates for web APIs that make it really easy to get up and running. Microsoft has good documentation and tutorials to help you get familiar with the technology. I would start there.