Can I pursue law after completing B.Tech?

Why not. You can do LLB even after B.Tech, because the minimum eligibility criterion is 50% (Varies from university to university)in any graduation. Admission to the same is based on entrance exams like CLAT ISAT, AILET etc. Admission Process: Admission is done either on the basis of marks obtained

Yes, it is very good. You can join Rajiv Gandhi Intellectual and properly Right Law (IIT-Kharagpur) for 3 years LLB. It is the best college for a B.Tech graduate.

Yes, you can pursue. You can become intellectual proprietary IP specialist. It is very well paid field.