Hello, and welcome to the forum (from a member across the pond, in the US)...
1. Which oil is better taking in consideration the 67k on board 0W20 or 5W30?
2. It seems that i'm missing my "maintenance mindr" on board. Don't know if it was not activated or removed at some point.
Is it possible to activate it again?
3. From where can I purchase a second key at a reasonable price....
1--Sitck with 0w20, no matter the mileage.
2--I'm not sure if the maintenance minder is the same on UK vehicles, as it is on the ones in the US, but if I understand your question correctly, the maintenance item code will light up automatically at the time it needs service. Here's a post with a little more info:
(also check the owner's manual--did you get one with your used CR-Z?)
3--I don't know about replacement keys, but I hear that you might have to get a 3rd mortgage on the farm to purchase one at the dealership. Read this post for some slightly better news: