Hi Booleano, for the hinge placement it would probably be best to start with the lid in its fully closed position like this:



Then to have 3 hinges you need a "hinge axis" line like Barry shows above, which should graze the profile curve in 3 spots.

When you want to set the case to its open position you would select the lid and run the Transform > Rotate > "Rotate Axis" command.

This one here, not the regular 2D rotate:


That one allows you to pick 2 points for the rotation axis, you would pick the 2 points along the hinge axis.

But in your case it is not possible to create the 3 hinges because your outline does not graze a common line in 3 spots.

It is probably a good idea to draw in the hinge axis early in your modeling process so that you can make sure you are making a shape that will work with 3 hinges.

For your current shape you would only be able to make 2 hinges with a hinge axis like this:



- Michael