How to make a GPS Speedometer?

My company car that I normally drive tends to have a "small" problems from time to time, the speedometer fall to 0 Km/h when driving (after some time it resumes again).

Normally this is not a big issue since if you know how to drive a car, you are not, I hope, always looking to the speedometer. You now more or less the speed that you are driving.

The problem present it self when you need to decrease speed to the road limit that you are entering and you notice that "the speedometer is down".

This presented like a good opportunity to build a new project, "The GPS Speedometer".

Of course the ideal solution would be, really repair the car or use a normal GPS or use an app with this function but what would be the fun in this :)

Hardware components:

OLED 2828 Display Module 
GPS Module with Enclosure
Dreamer Nano V4.1 (Arduino Leonardo Compatible)
3mm LED Pack (50 pcs)
perfboard
Hand tools and fabrication machines:
3D Printer (generic)
Soldering iron (generic)

Microcontroller

I selected the DFRobot Dreamer Nano V4.1 because it has a usb plug that I can use for power and a compatible breadboard pinout.
Check DFRobot Dreamer Nano wiki page for more info regarding this microcontroller

GPS

I'm using the UBX-G7020-KT, that comes with an integrated antenna and allows to change the refress rate until 10Hz(for this project this featuring can came in hand).
On the DFRobot GPS Module wiki page you will find more info regarding it.

Display

I wanted to have a good display without "blowing" the budget, my choose was
the OLED 2828 Display Module. Check again the oled Display module wiki page for some more info.

Power

The power for the system will be provided by the car cigarette lighter socket.

Casing

This time I when for designing a casing and 3D printing it. After some attempts, in the end I was hopping to get something like this.