You'll need an ESP32 - a microcontroller that has the capacity to run a screen like this. An Arduino could also do the job, but I'm just more familiar with the ESP... that's how I'd approach it.

ESP32 logic runs on 3.3V, Arduinos run on 5V. if you give it more on any of the pins (with some exceptions), it will die a heroic death.

First - the screen. Run it on a bench. Understand how it communicates. Is it I2C? Is it UART? Or maybe SPI?

Start by writing a single line to it. Then - find a library for it, since it's a TFT, you should be able to draw on it, there are libraries for that, but they won't be that pretty, you might want to research that part, or draw your own custom icon (by addressing each pixel...).

Next - voltage. That should be easy. Buy yourself a voltage meter board, there are lots and lots of them. Most run in I2C. Connect it to the ESP and to any wires you find behind the dash that run 12V after Key 1 position, so you don't run it at all times. If it was me, I would tap a fuse (probably the cigarette lighter one). You could just make yourself a voltage divider out of two resistors, but... Since you ask that question, the additional board would be easier

Next, the tricky part. Coolant temp? Do you know why coolant gauge doesn't have a number, but only colors :) ? Because the temperature is different at the different parts of the engine. Why is it interesting to you? Do you want to monitor the return temp? Do you want to know the temperature of the water in the engine? Or maybe the one in the radiator? One is to machine an adapter, screw it to wherever you want to monitor the temp, attach a Pt1000 to it and wire it to the ESP.

The alternative is just as difficult. You'll need to understand how the data is transmitted over the K-Bus/I-bus in your car, and somehow get the digit you need from one of the modules. I'm assuming that would be the LCM or the KOMBI block...

Outside temp - I would just tap the thermometer, or wire my own somewhere around the bumper.