Colleges in Delhi

Well yes, majoring in B.Tech after Diploma is always a good choice. You will get more knowledge of automobile in B.Tech. Also, you will get depth practical approach in B.Tech including industry exposures. B.Tech has more job opportunities than Diploma.

Well, there is no book available in market for LEET DTU exam preparation, but there are several coaching institute that provides coaching for LEET exam.
For more information, visit this site
http://www.dtu.ac.in/Web/Admission/b.tech(LE).php

You need to appear in DTU LEET exam to get admission in DTU for preferred branch.
For more information, visit this site
http://www.dtu.ac.in/Web/Admission/b.tech(LE).php

The Modart International institute conducts an entrance test of its own and you can find the details here https://www.shiksha.com/design/fashion-design/course/bachelors-in-fashion-designing-modart-international-delhi-east-of-kailash-176187
Although a student can skip the ENTRANCE EXAM if he/she has appeared for either NEED/NIFT (GAT+CAT)/PEARL (entrance)/SAT /CET GMAT/CAT/MAT. The score in one of these exams, along with a minimum score of 60% in 10+2 will determine your admission

Hi Piyush,
Try to score over 99.9 percentile in CAT for general category to stand a decent chance.

Dear Rashmi,
No college in India can give anyone 100% guarantee in placements.

No, you cannot apply in any of these institutes after the CAT examination. The applications are now closed for each of the three institutes.

It totally depends on your capability. If you are good at it, then you can do it.

The biggest benefit is that,
Some knowledge that you have can be incorporated into answers that will help not only the one who asked it but also the other people who search it on Google or Shiksha shaping their future without any hustle to decide.
Also, you get exciting things when you reach higher levels.
Start answering to decode them.