Don't paint a bike to enable the sale. This is a negative value proposition. Find a price where you thought the bike "would have" sold and subtract the cost of the paint materials, and you can even subtract some modest hourly value of your work. The result is your sale price for the bike "as is". You do the math, and then decide.

The headset ring is likely press fit, and can be removed by opposing blunt force applied from within the headtube and against the inner edge of the cup's flange. There are tools designed to accomplish this.

But we cannot know this for certain, because we can't see what you see.