Simone
Jamie
He most certainly is.
The only impact is that he training will slow down to only 3 points each time you hit the train button and if their contract expires you wont be able to resign them.
I can confirm the first part, he will race for sure.
I didn't know the second part tho! It's not written anywhere, I've been lucky enough not to experience it in first person.. I'm going to resign them for 50 races as soon as they get to 5 yellow stars then!
You can extend the contract anytime at any level as long as the old contract is still running, so no worries. But if you let the contract run out the driver leaves the team and since you can't hire any driver, or staff, of a higher level you can't rehire that driver again.