I have a gallon of Kilz Original oil-base primer. Can I use it as a primer on a small new construction outside? The primer would be covered by an acrylic exterior paint. Would the paint adhere to the primer and would the wood be protected?

I have a stained fiberglass door that is a walnut colour, however it’s too light. I would like to make it a rich dark brown. Can I paint over the stained door? What process is involved so that the paint on the fiberglass door doesn’t peel.