The size of the dashboard is not so important. It is more important what LEDs (smart or ordinary) you use and how many. Depends on whether any animations and / or effects will be used. If you are going to use regular LEDs and only show large 7 segment numbers, an Arduino Nano may be enough. However, you will also need a suitable power supply because many LEDs need a lot of power. You have not specified what exactly you will do and I'm just guessing.