Income Share Agreement-ISA Lawful Documentation And Liability

We are an early stage edtech startup offering onilne IT training to final year engineering students. We are exploring a business model of Income Share Agreement where we prepare students by upgrading their skillsets and in return student pay the fee after they get a job. The fee would be 12-15% of their salary/month. We have few queries about this: 1. Is is lawful in india to do such an agreement. Many companies are doing it but we still want clarity. 2. What documents should we ask students to furnish to make legally binding on them to pay after they get the job. 3. Do we need to take PDCs or cancelled cheques from them or pan card or other things 4. How do we really know if the student has got the job or not if they do not work in any of our affiliated companies. Your help will be really appreciated. We would want to also seek further expert service if and when possible.