1. (optional) Paint the particleboard and dowels. You can ignoree this step if you don't care about the colour and appearance.
3. Drill the holes. Make sure to use the correct drill bits for the dowels. This is a very tiring part
I pre-drilled with a small drill bit to make sure correct position. You can ignore that but directly drill on the board with a bigger size drill bit.
Below picture is the small pre-drilling holes.
5. (optional) Seal the particleboard edge with Iron-on Melamine Edging.
Update: Here is the picture of the rack with thread spools: