Polytechnic

Yes, after your Diploma in electronics, you are eligible for this course.

No, at this rank there are only about 60% chances for government colleges. Your rank should be around 2500.

Yes, you can get but your 12th should be completed and also, you have to crack the entrance exam which is conducted by the state government.

If you want direct admission in any private college, then you can directly visit and you will get admission in any private college. But if you want admission in any government college, then you have to crack the entrance exam.

Yes, you are eligible for CNC and Polytechnic too after ITI. You can apply for any polytechnic college.

No, it's not necessary but it would be better for you if you have a laptop.

Yes, after 12th, you are eligible for lateral entry means direct admission in the second year, but you have to crack the entrance exam with a good rank because every branch has only 6 seats in the second year for lateral entry.

At this rank, you'll get good colleges. I am listing some colleges; please do check the list below:
RVS College of Engineering and Technology, Jamshedpur
ICFAI University, Jharkhand
University College of Engineering and Technology, Vinoba Have University, Hazaribagh
Cambridge Institute of Technology, Ranchi
RTC Institute of Technology, Ranchi.

Polytechnic is also a Diploma course, if you want to go for technical fields. The eligibility for getting admission in a Polytechnic college, is you must have passed class Xth from a known board. Other than this, you have to fill out the form for Polytechnic exams, which are held for the selection of students in Polytechnic colleges.

The fee structure for Polytechnic course is around INR 30,000 per year.