Create me a Blender script/addon

Hi!

I'm wanting a blender script/addon made.

I want to be able to add custom data to mesh faces, then export that data as a json file to be used in a custom program.

- I want to be able to add json data to each mesh face, by selecting a single face and assigning a value aswell selecting multiple faces and assigning a value.

- I would like a export button to be able to export that custom mesh data, it would export to a file which you could name as a simple json file as a array. e.g. var customFaceData = [
{
customKey: "value"
},
{
customKey: "value"
},
{
customKey: "value"
}]

If there is no data for the face a empty json object should be created

- It would also be good if I could somehow visualize the custom face data on the actual mesh, this is not a requirement though just a want (e.g. show faces which don't have empty values)

Let me know your thoughts!

Thank you very much.