I have no formal CAD experience, I just wanted to build some stuff with my 3D printer.

If you are going to experiment with FreeCAD, I highly, highly recommend starting by learning about parametric modelling. Define everything in the spreadsheet, and relate all of the sizes to each other.

If you don't, it will be a very frustrating experience when you realize halfway into your design that some earlier piece needs to be tweaked, and your whole model falls apart.