Got a call from IIM-Rohtak, so should I presume I'll get calls from all new IIMs? Also, what are my chances converting it?

Yes, there is high chance that you will be getting calls from most of the newer IIMs if not all. However, based on your profile it won’t be easy to get into an IIM. You might have to work extra hard for your PI round. 

Prepare for the interview by availing of some professional help. The competitions for IIMs are tough and should not be underestimated. One excellent way to prepare for your interview is going through interview experiences on Pagal Guy. It provides elaborate interview experiences of converted calls. You may also join the mentorship program at new IIMs.