JEE Main

Yes, there are 90% students in NITs who opted for CSE and are studying it for the first time. There is no problem with that.

No, for being a general student, you need at least 180 marks for securing a seat in IIIT G or a rank of 25000 at least.

I would suggest you to use the college predictor from Shiksha which is mentioned in the link given below:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

It is difficult to say as it is different for different states.
Kindly find this in the official link of JEE Mains given below:
https://jeemains2018.in/category/state-wise-colleges/

Go for MBM Jodhpur. NIT Manipur is at very lower rank, whereas MBM Jodhpur is a top-ranked college or Rajasthan. It is also a favourable industrial location and better than Manipur in terms of placements and academics. Best of luck.

Yes, you are elegible for it and you'll easily get CSE or your desired branch in it. Best of luck.

No, you can get admitted to IIT if you clear JEE Advanced and You get to sit in Advanced only if you clear Mains. If you failed to get in Mains, you will not be able to move further in the process.

Not, likely. You may get into lower NITs such as NIT Pondicherry and NIT Manipur. Choose them if you find them worthy. Else, chances are less with decent branch.

For architecture, you may face a hard time with colleges as if you are from General. Although, suggesting you to get into private colleges which though you can apply having their own entrances. Also, keep NATA and other exam options with you to have a wide range of opportunities (colleges).

You will likely GET ECE in one of the NITs such as of Jaipur, Surat, Silchar, Bhopal and Nagpur. You may also get chemical in Warangal and mining in Surathkal. For CSE also, you can try the first four NIT out of which, NIT Jaipur is most likely. Best of luck.