1. You can make use of the parse delimiter rule with the comma separation as the delimiter and you can map the three values to the properties to a page (Or) you can build the Pega function using the java split method and call that from your activity with the expression builder or call-function method and set the properties.
2. Once you have the page you can use the JSON Data Transforms with the serialize option to convert that into the JSON. (Or) you can also use the function pxConvertPageToString (tools,page,"JSON").