Can you guys suggest if I need to surrender my certification of practice before going in house? What is the procedure of doing so? How many takes it might take?

You will have to inform the Bar Council about your transition and ask them to move your name to the register of non-practising advocates.

Yes if you’re contracting employment. No if you’re a retainer. It’s a simple form to fill. Once you want it back. It’s another simple form.

These days employers are reluctant to employ in-house counsel on retainership basis as it attracts 18% GST that's applicable on reverse charge basis. It increases the cost of hiring by 18%! From the lawyer's point of view, a retainer arrangement is better because you pay income tax only on 50% of your income/salary; the rest of your income is presumed by law to be the cost of running your practice.

Nobody cares. Don't do anything. Just relax.

Or make your job as a retainer and forgo some corporate benefits like PF.