JEE Main

https://jeemain.nic.in/WebInfo/Handler/FileHandler.ashx?i=File&ii=86&iii=Y
You can download the above link for detailed syllabus.

Negative marking is also there. So, overall, JEE Mains is quite tough than CET, but the ratio of toughness depends on your preparation. MHTCET is focused on testing the breadth of your knowledge and JEE Mains is focused on testing your depth of knowledge; so don't compare their difficulty levels.

In JEE 2019, 12th marks don't matter to it but yes, you have to secure minimum 75% marks in the board exams, only then you would be able to get admission in the NITs and IITs.

I'll prefer you to join any other coaching institute like Allen and Resonance as the coaching institute mentioned by you is also quite good. But the main problem is that their passing ratio is not that good.

The eligibility criteria for JEE Mains counselling is to just appear for the JEE Mains paper, whether you have qualified the exam or not.
You are eligible for the counselling, but yes, if you haven't secured 75% marks in the boards exams, then you are not eligible for admission in any of the colleges through Mains counselling.

Yes, it's hard as JEE Main but not as hard as JEE Advanced. If you want to crack this, you have to clear your all concepts of 11th & 12th standard.

For getting admission in an engineering college, you have to apply for JEE exam. If your JEE Mains score is low, you can get a low NIT, but there are less chance for you to get a good NIT. Apart from this, you can get good government colleges in your area. To get admission in those there is a different counselling form for every state.

You have to secure under 7500 rank. Only then, you will be able to get the admission in the main campus with CSE branch.

You have very less chances of getting a government college. With this rank, you can get some of the good private colleges, but getting any government college is very difficult, if you are from general or OBC category.

Yes, you can get a government college with this score, but in the central government colleges, there is no defense quota.