1. Tasks have local data inputs and data outputs (BPMN2 spec). You have to map process variables / data objects to Task data inputs and also if needed map Task data outputs back out to process variables / data objects.
jBPM Designer also has an intuitive data input / output editor similar to the process variables editor which you can use to visualle do the mappings
2. Process variables, data objects, data inputs/outputs can have a type. This can be a custom type (type of your spefic class) as well, so you should be able to use that in a form.
HTH