NLU Delhi (NLUD) - National Law University

All candidates, other than those applying under the Foreign Nationals category, should appear for the All India Law Entrance Test AILET and selection shall be solely on that basis. Candidates should score at least 40% of the marks in the AILET (30% for SC/ ST candidates).
In order to appear for the AILET candidates should have passed the 10+2 examination and scored a minimum of 50%. However, candidates appearing for 10+2 examinations in the year of the AILET can also apply, provided they meet the above eligibility at the time of admission.

Yes sure, you can rewrite your 12th and CLAT at the same time. You can appear more than once for CLAT provided that you have appeared for 12th and passed.

No, NLU is offering a three year LLB course. All the NLUs have integrated LLB course along with Bachelor of Arts, Science and so on.

NLSIU is the top NLU among all.

Some private colleges are good but they are not that preferred compared to NLUs.

I guess the colleges which offer admission without entrance must be state board colleges or college not too specialized in teaching law.
I would advise you to take admission in some good college with entrance process as they are said the one with a good reputation.

It depends on your rank and interest and CV and what had you done in your college life. It's around 10 Lacs per annum, I would say.

Admission is only through Common Law Admission Test, also known as CLAT examination.

Yes, you can. You need to submit your transfer letter and permission from your previous university while joining the new one.