help with diy body repair

[jess28]

I recently scraped and dented my (nearly new) car's back passenger door and wheel arch against a post causing scratches on the door, a paint chip on the door shut (which is now beginning to rust), a slightly bent wheel arch and bent plastic moulding that has started to come away from the wheel arch.

I took the car to a few bodyshops but was given rather excessive quotes (ranging between £800 and £1600), so I've decided on diy repair for now, mainly to prevent rust from setting in on the scratched surfaces. What I thought I could do is sand down and seal the chip on the door shut by applying touch-up paint and clear coat, and apply clearcoat over the scratches on the door.

My questions are:

1. Is clearcoat sufficient to seal the scratches on the door and prevent corrosion?

2. Will I have to apply primer on the chip on the door shut? I can see signs of rust at the edges of the chip, which suggests to me that the metal has been exposed. On the other hand, the surface of the chip is greyish in colour, which makes me think it's the basecoat that has been exposed, not the metal. If I have to apply primer, can anyone suggest a product in liquid form as it's easier to apply on a small surface area than sprays?

Any help with these questions will be most appreciated.