Properly align the Ikea Pax wardrobe

Hello guys - a question for the pros: how would you align a wardrobe?
Yesterday I assembled all my Pax and roughly placed them in position. And now?
First level it with a spirit level, then fix it to the wall, then install the inserts (drawers, shelves, clothes rails, etc.), or install the inserts first, then level it and fix it?

The installers at our place leveled the cabinet before they installed the doors and shelves. They did not attach it to the wall after consulting with us, as we do not have children who could use the cabinet as a climbing frame.

After aligning with the adjustable feet, the side panels should still be supported underneath (especially if the cabinet is not attached to the wall), otherwise the bottom board of the PAX can easily break out.