Thanks @Xulfiqar, @capsat & @tintin1. I've got my answer.
I fully understand (and agree to) your criticism on these marketing words like "doctor driven". However, in this case I know the doctor closely and I know that the car has been kept and maintained properly.
I agree that user manual should always be followed, therefore am going to pour in 5w30 oil. I have bought Total 9000 future 5w30 (fully synthetic) oil. I hope it is not a bad choice, if not the best? and I also hope change interval of 4-5K is appropriate?
Thanks for your input!