IIM

Most of the colleges now a days are looking for diversity in academics and work experience. Considering your graduation in BBA and arts background, you have very good chances of getting calls and converting them. So, keep your hopes high.

Check out the links below for all the details :
https://www.shiksha.com/college/iim-Ahmedabad-indian-institute-of-management-iima-vastrapur-307/admission#admission
https://www.shiksha.com/college/iim-Bangalore-indian-institute-of-management-iimb-bannerghatta-road-318/admission#admission.

There is no steadfast rule as such for selection. But, if you have 90% above in class 10th and class 12th, you will get maximum marks for that section, and even if you have decent CAT score, you can convert them. If you have great CAT scores based on category, 80% above in both class 10th and class 12th will suffice.

If you have all the necessary documents related to your job, then you can include the same as your work experience for taking admission to IIM.

Sorry, but it's not possible to get IIM with this score. I would suggest you to fill form for below colleges:
1) BIMM, Pune
2) ISBS, Pune
3) Jaipuria, Noida
4) ITM, Navi Mumbai

Hello, No it is not necessary.

Hello, You can do MBA in operations major which will be more in line with civil engineering.

If you are a topper, then it is a cherry for selection but if not try to score excellent in your CAT exam. Maintain 80 above score in UG if you want to get selected.

Yes, you have chance to get into IIMs by getting 99.99 percentile.

It basically does not matter up to certain extent but you need to do well in you entrance exam to get admissions in IIMs.