Law

You went for the right decision. Just because you have dropped a year, make sure you hit it this time. Syllabus of CLAT is somewhat different for the students who are from the science background. Dropping a year and focusing completely on NLUs is a worthy decision.

If you are pursuing diploma in mechanical engineering then you get jobs in mechanical fields like automobile, production, maintenance etc. There are lots of opportunities available in engineering field. If you pursue B.Tech after your diploma then you may get more opportunities and good career start after B.Tech.

Yes, IPU offers 3 year LLB course.

Below, I have attached a link for top 10 law college in India offering 3 year LLB programme.
https://www.google.co.in/amp/s/blog.ipleaders.in/three-years-llb/amp/

Of course, you can but it would take hard work accompanied with smart work.
Here are some clat preparation tips which you can use to score well in clat 2018 entrance exams.
For logical reasoning preparation: http://www.clearlawentrance.com/2017/12/logical-reasoning-preparation-tips.html
For English Preparation: http://www.clearlawentrance.com/2017/07/clat-english-tips-and-tricks.html
For Maths Preparation Tips: http://www.clearlawentrance.com/2017/12/maths-preparation-tips-for-clat-and.html