B.Tech Eligibility

Yes, you are eligible for a seat in a college under IPU. Your rank is sufficient enough for that.
So, go for the counselling and also do keep some side options.

Go for B.Arch as you have got a good rank. You can get a good NIT for B.Arch. But choose B.Arch only if you are interested in architecture.

There is no need of 12th marks for JEE 2017. Based on your JEE score, you will be directly awarded the institute. For getting into NIT-Warangal based on your category, you can check it on www.josaa.in (opening and closing rank 2016).

Yes, you are eligible to take admission for B.Tech in a private college.

To take admission in IPU, you have to qualify the CET exam. After that, participate in the counselling process.

Following are the best options for you:
Girijananda Choudhary Institute
Assam Engineering College
Jorhat Engineering College
IIT-Guwahati

The eligibility criteria for B.Tech at Nirma University are:
1) Candidate should have appeared JEE (Mains) 2017 (For 35% All India Seats and NRI Sponsored Category).
2) Candidate must have passed 12th Science Examination with Physics, Chemistry and Mathematics with the percentage of marks as to be decided by the Government of Gujarat under the rules of admission.