@Singed said in Create a simple managment application, where to start?:

My question is: what would be your recommendations for this project? For example, which tools or approaches should I start with, and which ones should I avoid because they might give me a hard time later? In example, start absolutely using this "xxxxx" because you will have hard times instead and similar.

In general:
To re-build a UI design similar to the one shown in your screenshot, I would go for a QtQuick/QML app. It is more modern looking and easier to integrate fancy animations, visualizations etc....
... unless something prevents you from using QML or you want to go for a more native OS looking desktop QtWidgets app.
Are you targeting one platform only or should it work on multiple?!

Then, depending on your knowledge, the next question is: C++ Qt or one of the Qt wrappers like PySide or PyQt (Python)?

Also, I would like to know if there are modern, free graphics or UI templates that I could use as a starting point or even as a final design. Some ready-made designs look very nice, but they are not free. Is there a free database or repository of Qt designs that I could access?

There are some, but mostly you will find more like "parts" online, that you can put together.
If you are looking for some nice stylesheet, you will find examples.
Or if you are looking for sidebar widgets, you will also find examples on GitHub or DIY tutorials online.
But not "your" complete design free to use. Haven't seen something like that.

Most of the UI can be done using Qt's standard widgets (or QML elements): Different Views, Menus, Buttons and other controls etc....