IIM Eligibility

Mainly sales and marketing has the hierarchy of Area sales manager, Regional Manager, Country Head, etc.
And in marketing, you can be a Brand Manager wherein you'll be responsible for P&L of a brand or a category.

IIMs consider only graduation degree marks beside 10th and 12th marks. Your B.Tech score will be considered. Process and weightage of marks differ every year. You may look at IIMs website for details.

You are eligible for appearing in CAT to seek admission in MBA provided your university is recognised and you complete B.Tech with greater than 50% marks.

It is bit difficult with the percentage but not impossible. Focus on CAT percentile (above 99) and why you are a best candidate through GD and PI.

IIMs consider acedmic performance in 10th, 12th and graduation degree for shortlisting candidates for GDPI in addition to CAT score. You may refer to following article for details on IIMs shortlisting criteria for candidates who clear CAT:
https://www.shiksha.com/articles/understand-the-short-listing-criteria-of-all-iims-blogId-5379

Dear,
To get a seat in IIMs does not only depend on your CAT percentile but also on your your academic record, overall personality, commitment, communication skills, knowledge and positive attitude.
All the best.

Diploma in Engineering from polytechnic is not a graduation degree. You will not be eligible to seek admission in MBA unless you complete your graduation degree. If you have done diploma after 10th then Diploma marks may be taken against 12th marks. But if you have done Diploma in Engineering after 12th then 12th marks will be taken.

Dear,
It all depends on your CAT percentile, GD and PI session performance.
Your positive attitude, commitment, learning personality and a good foundation of your graduation subjects especially, economics will give you more chance to get selected.
All the best.