I need to paint a metal door and some metal weights.

The door is already painted and in very good condition except where
there are some nicks and scratches.
The weights have been used over the past 20 years but are in decent
condition.

My question is, do I have to take the door and weights down to shinny
metal, prime and then paint, or can I maybe take the scratches down to
bare metal, sand the rest of the paint, spray a primer and then a top
coat.
The weights are cast iron and only a few of the very oldest have even
a haze of rust - easily removed with just a light sanding of 600 grit
paper.
The nicks in the door appear to stop at the primer or the color before
the current color. But the paint doesn't have that look of having
1000s of layers on it.

Anyway, any suggestions on how to proceed? I would settle for minimal
effort for the best look. I'd rather not send the items out to be
acid dipped or spend a week stripping them with chemicals.

Thanks
RC