first start with having a budget
Radio Unit is main thing.
Steering remote comands (not nessery)
you need to have or decide what what kind of phone do you want to use/or tablet ( i use samsung note2)
then you will need some one who study or know to do things with Plastic. (i went to my friend who was studing Academy of fine arts)
he take mesurment of phone and take some samples and make cover on top of the oem radio screen.
after that you enjoy
For all of this i spend
HU Alpine IDE 178BT 220Euros
Comands 60Euros
Making of display with painting 60Euros
Mobile phone 350 Euros. Actualy you can use any phone with android system that have large screen and it is for daily use so it is not expense
Here are some thnigs on YT that can guide you ... but i think that ipad mini is too much for Clio on board system....
https://www.youtube.com/watch?v=zDThVZzVtqw