JEE Main

Yes, you can get admission.

Use the Shiksha college predictor for getting some idea about college that you might get through your valid JEE marks. For your help, I had provided the link. Click on it:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

You can apply for private or autonomous campuses all over India. For those colleges, NATA is not needed.

You need to give the NATA exam (preferably before the end of May) and then in the month of June-July apply for the admission process of DTE. If your NATA score and 12th percentage are really good then you might get into Sir J.J. college of Architecturing.
Admission to B.Arch. is done on the basis of valid score obtained in NATA/ JEE Main 2018.

Yes, you can expect a seat in any of the NITs. Warangal and Raipur are having more chances.

Hello,
I hope you are doing well. No, you can't get the seat in any NIT whether they have vacant seats or not because they will prefer vacancy in seats instead of getting admission of low rank candidates. So don't think for NIT hamirpur if you have low rank you wont be able to get this NIT. Go to different private colleges you will get.

For mechanical branch it was around 500-1000 state merit rank. For comps it was around 1600-1800 and for IT elex ExTC it was around 3000-3500 till CAP2 with percentile of around 96. If you have patience then i will suggest to wait till CAP3 ie. Counselling round as cutoff there was around 6000 for comps and 11000 state merit rank for IT. So if you have less score then keep calm and wait till CAP3. You will easily get into the college you want.

It completely depends on your choice what you want to do in the future. B.Sc. Students mainly opt for higher studies, research whereas B.Tech students go for placement, startup, higher studies and MBA. Choose wisely what you want to do.

Sorry, these marks are comparatively lower than what is needed. For OBC , it's 100 required for getting into core branches of MITS Gwalior and around 80 for non-technical branches. Kindly try for ITM Gwalior, LNCT - Bhopal, GECU - Ujjain (if you need only govt., else not).
Best of luck.