Custom Visual - Font size showing in percentage

I had the same problem. It turns out the property name has to be EXACTLY "fontSize" for it to work. Like this:

            "properties": {
                "fontSize": {
                    "displayName": "Category Font Size",
                    "type": {
                        "formatting": {
                            "fontSize": true
                        }
                    }
                },

In your case, the problem is that you would have many "fontSize" properties in the same object group, and this is not possible, so you'll might have to rearrange your options.