what things to model separe?

So i am modelling a Renault Kangoo and somebody said that check a car what thing i can remove from the car front/back bumper, doors etc. So if i want to have the car that its back hatch can be removed i need to make it separe?

 

If you want to have any part be modifiable independent of others, then yes, they need to be separate

 

look at the covet .dae in blender, there's your parts list

 

alrighty then thx for a good answer