IIT

Yes both IISc BANGLORE and IIT's particularly IIT Delhi offers M.Tech in VLSI where IISc Bangalore offers detailed oriented research and IIT Delhi have industrial connection.

GATE is an entrance exam for M.Tech in various NIT's and IIT's. For general category the minimum score required to get into one of the top IIT's or NIT's for Mtech is in the range of60-70 out of 100. Well the specific cut off's for each university will be released once the results for GATE are officially announced.

Yes, IISc Bangalore is said to be harder than IITs in some of the programs, particularly in admission and in the academic aspects. The institute is distinguished by paying high emphasis on research, innovation, and academic excellence. Only the candidates in the highest percentile in exams such as JEE Advanced, GATE, JAM, or KVPY are accepted in IISc. It is more difficult than most of the IITs as it has its recognition globally and because of its high patent record as well as its emphasis on in-depth scientific knowledge.

Options depends upon you category and homestate, so complete your question. 

You JEE MAIN rank is too good . It guarantees you good seat in good college.

For IIT seat it will vary from category.

You can get one of the top 10 IITs for 747 marks.

As cutoffs change every year you have a high chance of making to top 10 IITs for 747 marks for CS branch.

You should put 

IIT Bombay, IIT Delhi, IIT Madras, IIT Kanpur, IIT Roorkee as your top targets or preference.

Also you can get IIT Kharagpur.