JEE Main

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.

Kindly mention your score or rank and category.

No, the last year cutoff for general in EEE was 4661 - 5309 (open and close) and in ECE, it was 3807 - 3982 (open and close).
Try for other options. All the best.

No, as the admissions are only through JEE Mains. Though, board's marks are only for the eligibility.