Be careful about where you get your information. What you are doing is technically finishing wood furniture. The type of painting you will be doing is not the same as painting walls, which could be why you're getting so much conflicting information.

It sounds like you're dealing with muddy water, so I'm not sure how much help it would be to share what I would personally do because I dive in head-first on things and learn as I go. Maybe get a piece of wood to test on and see if you can arrive at the finish you're looking for?

You don't need to apply anything like poly, you'll just apply a topcoat. For your purposes your paint is your finish. If you decide to go with an oil-based finish then understand you will be creating a piece of fine furniture, and you should supply yourself with enough time and patience to learn such a craft. Don't rush that process.