Hi Nico, and welcome to the club! The Navi unit will require the loom as the connections will be different. Unfortunately most used units don't come with any wiring, so you'll find it difficult to install. My advice would be to go for a good quality branded aftermarket unit instead as it will be much more straight forward to fit.
Looks good and a bargain to boot - congratulations Glad to hear that everything still works - my rain sensor doesn't and on cold mornings, I keep getting low pressure warnings for the tyres Neither are a problem but the tyre pressure warnings are a pain in the hole