Used car purchase and repairs

Hi, i am new to your software so i apologise if this is a newbie question.
I am running a small vehicle repair and sales company, what category would vehicle purchases go under as they are stock and not business vehicles? also i need to account for additional costs when selling the car i.e MOT,repairs, spares purchase etc would these go under motor expenses as they are on vehicles or other categories?

for tax purposes i understand that it is the profit that is taxed, so parts and repairs need to come off of any final sale price to identify the true profit. what is the best way to set this up.

and again i apologise if this is a rudimentary process.