3D question-what files do I need?

KiCad can use step files but you will most likely need to align the models to the footprint either in a cad program and reexport as step or in the footprint settings. The former is quite easy with Freecad and the kicad-stepup workbench. The later will be finicky and could require you to update all footprints depending on how the step models are made.

Further reading:

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