Hi Jeet,
I have received my NOI last week, same as your NOC, i have been processing my application through consultancy. To answer your question, see response below
1. There is no mandatory that the job offer is required, if you have, chances will be more to get nominated with less time
2. Reference letters are not given by the companies in India, you can submit the offer letters, payslip, relieving letter and a self declaration stating the job roles and responsibilities and no of hours worked. This will suffice the requirement that is mandated in the checklist