2 options of either assembling it as you go or all in one piece.
Use the 5.5*2.1 DC Power splitter to get power for the fan from the origin power supply
BOM
5.5*2.1 DC-022B Female Jack
5.5*2.1 DC Power Splitter
24V 4010 Fan
KCB11 Switch
4x M3x16 flat head screw
4x M2x6 self tapping screw
4x M3 hex nuts