Solved

Car Design

1) the email you receive after each race notifying you of points unlocked in respect of the areas of the car you ticked the boxes for in "details". 
For example +4 points for the 4 parts I've focused only on however I've seen before that I got +12 previously when I had all car parts selected? By only getting +4 it doesnt mean my car is not as developed as if I got +12?

2) following from point 1, do the bars in car details only move after each race or do they gradually increase over time between races?

3) car competitiveness at start of each season is it randomised or does it depend on your staff?

Simplified answer:
2) The bars increase either through researching competitors, applied after each race. Or, by you manually adding design points, which you receive per race and can be increased in HQ
1) Research points gained depend on the difference between you and your best competitor for the stat(s) selected. Also, the star ratings of your CD & TD, try to get these up to 5 if possible but it's relative to your level so they'll decrease as you level up. Selecting more just spreads the impact around. The reason you may be seeing differences is either * levels changing or the research gap between you and the competition
3) Every race contributes points to the next season's design based on the level of your CD and their strength & weakness

I have never heard before that your suppliers affect your starting car design. How does that work?

Please Kevin copy your posts in a new thread and lock it on top of the board. This is the best tutorial about design. Complete and clear

Ohh, so you don't mean that they change the 'core' design of the car based on what suppliers you had last season? Sorry, the way you worded it made me think they affected the design in a similar way to what your staff do, not just the bonuses they directly add. That'd explain why I'd never heard it before! XD