Solved

Chief designers.

Hi.
Silly question. 
I have 1 chief designer, 1 technical director and 1 doctor. Do I  need a lot of reserve staff?

A level 16 team seem to have better development than me at level 20.

Having multiple TD or Doctor is useless, they do not change development if they are 5 starts.
Multiple CDs can help because depending on weaknesses and strengths you can develop the car more.

Read the guide about start of season design for nore informations.

Thank you.

You're welcome :)
Sorry I couldn't provide the link directly, I'm using my phone ^^