Test preparation

it is up to you and also how strong your fundamental skills are . I personally think, 11th is a bit early to start coaching. the syllabus for the foundation level in CS is manageable without coaching provided that you have a good commerce background. just look at the syllabus and decide for yourself.

Go for arihant publication books

Physics is a very tangible subject. You can actually see everything happening around you. When we are not good at something it represents our disinterest in that thing. Try to develop your interest in it by strengthening your concepts. Solve the easy questions first. I recommend you use the book HC Verma. After every chapter it has concept based questions which are the best to test whether you really understood the topic.

CA is the one of the most difficult course of commerce
It is also highly respected and good professional course
Ca can work in auditing , taxation and various matters like valuation , merger, credit rating
There are 3 levels CPT, IPCC and Final
CPT can be pursued after 10+2
IPCC can be pursued directly after graduation
It also requires 3 and 1/2 years articleship training uder practicing CA/CA firm

It is called SOP Statement of purpose. you can get guidelines in shiksha website itself as how to write an SOP. it is statement about you and you can describe how did you get in to this particular area of study and what is your ambition in life.
There is also a website called statement of purpose.com you can google and get it.

Yes you can if u r superhuman

CBSE marks are used as eligibility criterion for JEE Advanced. The candidates should satisfy at least one of the following two criteria for admission to IITs and ISM:
(1) Must have secured at least 75% aggregate marks in the class XII (or equivalent) Board examination. The aggregate marks for SC, ST and PwD candidates should be at least 70%.
(2) Must be within the category-wise top 20 percentile of successful candidates in their respective Class XII (or equivalent) board examination.