B.Tech

In June or July. Keep your eye on www.jmi.ac.in .

No, first complete B.Tech then try for a Diploma course.

Unless you pass all your subjects, you can't. Try to answer on demand from NIOS and you will be able to get admission.

WBJEE is better than ComedK. ComedK is just for private institutions in Bangalore. WBJEE is a state level entrance exam.

Yes, some universities in Australia and London offer B.Tech.
Even my friend got admission in a college in London after completing Diploma.
In Australia, the University of Sydney offers B.Tech through lateral entry.
In India, except for central government controlled and few private universities, all uni

By taking JEE Mains followed by JEE Advanced.
You will only be eligible for JEE Advanced if you clear JEE Mains and only if you get good rank in JEE Advanced, you will get admission in IIT.