MCA

This would depend on your interest area and career aspirations. If you are keen on the technical side, MCA is better. However, if you want to move into the Non-Technical / operations /general management side then MBA is a better option.

No, you must clear the cut-off of NIT Calicut. Otherwise, you are not eligible to take admission.
Good luck.

Hey,
You can prepare for NIMCET. It is a Common Entrance National Level Test, conducted by any of the NITs, for admission in their MCA programme. It is the most preferable exam and the key to admission into NITs for MCA.
Good luck.

Yes, you can get but you have to crack the JEE Mains entrance exam.

No, after BCA, you can take admission in MCA first year, not in the 2nd year (lateral entry). If you are interested to take admission in the 1st year of MCA then you can take admission.

NIT colleges are the best colleges for MCA. NIT colleges ranking for MCA (you should fill in this order) NIT Tiruchirappalli (Trichy) NIT Tiruchirappalli (Trichy) The top most college for MCA in India. NIT Surathkal. NIT Warangal. MNNIT Allahabad. NIT Calicut. MANIT Bhopal. NIT Durgapur. Top MCA Colleges/Institutes: ITM University, Gwalior. Jamia Millia Islamia, New Delhi. IIT Roorkee. NIT, Surathkal. Birla Institute of Technology (BITS), Ranchi. NIT, Rourkela. PSG College of Technology, Coimbatore. Vellore Institute Of Technology, Vellore.

MBA:
MAT exam is available 4 times in a year. February, May, September and December. And, CAT 2018 will be held on 25th November.

Hey Ashwini,
Lateral entry is possible in MCA.
Lateral Entry Scheme:
Admission to Third Semester:
Admission is open to those candidates who have successfully completed their graduation in any discipline from a recognized along with 1-year PGDCA/PGDIT/GNIIT or its equivalent.