Hi there,
jBPM5 provides you the APIs to create your custom forms backends interactions. For the front end you can choose the technology that you want.
About the simulation, it depends on what you want. You can create Mock/Test Workitems and run your process in Test Environments to be able to see how the process behaves before putting it in production.
Please, let me know if I can help you with more doubts, that you have in order to adopt jBPM5.
Greetings!