No supports needed for any of the parts.
The magnets I used are 5x1mm. They can be found on Amazon:
https://www.amazon.de/gp/product/B07T13H3R5/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
You need a total of 48 Magnets
If you want to remix this, you can find .step and .f3d files on my github:
https://github.com/oemeruelker/wingspan-organizer
For a variant which can hold sleeved cards, check out this remix:
https://www.printables.com/model/230275-wingspan-base-ee-oe-sleeved-insert
If you want to support the creation of more organizers like this, you can
tip me here: https://ko-fi.com/realoneup
The author hasn't provided the model origin yet.