My experience is based on cheap particle board bookcases that I painted white. From everything I read prior to starting, durability and looks was solely based on priming the piece very well. I did two coats of primer. I also used a high quality paint - I believe it was Benjamin Moore and made for cabinets (I want to say it was some type of leveling paint?). The drying/curing time between coats was 24 hours and I did at least 3 coats. Maybe more? I thought they turned out amazing! It was worth it to me to keep the existing bookcases (rather than buy new) and all it took was my time. I did not top mine off with any type of clear coat, but it definitely wouldn't hurt for you to do so!

Clean the surface, give it an overall light sanding, feather any chips/peeling or fill with Bondo and sand. A primer over any bare wood or Bondo, might as well do the whole surface. Again a very light sanding, remove any dust. Two coats of an oil, waterborne alkyd, or paint made specifically for cabinetry (don't use ordinary house paint).

Ben Moore has some advice here: https://www.benjaminmoore.com/en-us/contractors/job-solutions/professional-how-to-guides/cabinet-refinishing

With a quality paint, there's no need for a poly top-coat.

I received excellent advice from a local hardware store that was a very busy Ben Moore dealer. If you have a place like that, you should visit. From the prep, to correct primer, to best paint and applicators, comprehensive advice is the key to success. A general observation as a rookie painter is that brushstrokes look awful unless you're going for a rustic look. Talk to someone about avoiding that with the right paint, and possibly using small foam rollers, or even spraying. Supposedly, paints like BM Advance provide a better finish for cabinets, so that might work. A good paint store can make a spray can from your choice of paint (with limits). For nightstands, not much is needed and the expense might be worth it for a smooth finish.