NIT

What is your name and where is your home state I don't know. You got 19k in JEE Mains paper 1. It is not a bad score for 2018. You will surely get NITS, no doubt about it. But, 70 percent marks in class 12th is arising question, so you may wait for JEE percentile.

Yes, you are eligible through your marks. Though, I suggest you to check your eligibility through your board marks, as the minimum marks in most colleges in category students are around 65%, so there you can lack. Otherwise, you are clear. Best of luck.

For getting into a good NIT for general and with a good branch, the least you should have is 195. Below these marks are for category students to get admitted into. Best of luck.

If this is your all India Rank, then you'll definitely get in any of the top colleges. If this is your category rank, then you can expect in top 6-11 NIT's. Also, you can go for various good autonomous institutes with home state quota. Refer NIRF rankings for engineering for their performance analysis.

Hello Prabhakaran,
You may use the college predictor tool form the link below to know your chances of getting an NIT or other colleges :
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.

Yes, you are eligible to do B.Tech, but you must have a Diploma in mechanical engineering.

Yes,
NIT Surathkal is better than the other two NITs. Actually, NIT Surathkal is in 2nd position in NITs across India.

You might have a chance if you have any reservation criteria else give it a try. You have very great chances to get into this institute, with this rank. Attend the counselling and choose your options appropriately. Try Shiksha college predictor for better analysis.

You can check it out here and mostly it depends on your category but give it a try.
https://googleweblight.com/i?u=https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor&grqid=UQPd1RND&s=1&hl=en-IN&geid=1031

You might have a chance if you have any reservation criteria else give it a try. You have very great chance to get into this institute with this rank.
Attend the counselling and choose your options appropriately.
Try shiksha college predictor for better analysis.