Painting old builders grade cabinets.

Hey so I am currently painting my kitchen cabinets. They are over 20 years old and I live in the south, so over time the humidity has caused little ridges in the surface. I have done one door with a different brand of paint and it took forever! I’m wanting to do the bottoms in all in one paint, but I’m wondering if anyone has suggestions about how I can deal with the ridges in the cabinet doors first. I did wood filler on the one and it definitely helped, but it was also quite the undertaking. I don’t know if the photo does the ridges justice, they’re small but all through the surface. Also how does all in one paint do in a sprayer? Thanks for any insight you have, this is my first time doing kitchen cabinets so I’m a bit nervous.