You can create your GUI in C++ using the Qt GUI tool kit.
Do the bulk of that work on your PC (Windows, Mac or Linux).
When that is designed, coded, tested move the source code to the Pi and compile it there.
Qt GUI programs can be run full screen without X Windows. The GUI coming up fast when you power up the Pi.
However, I agree with TimG. Create your user interface as a web page.
I have been experimenting with this approach here: https://xn--2-umb.net/login
source code here:. https://bitbucket.org/zicog/propanel
Memory in C++ is a leaky abstraction .