Hello Dhruv, 

If you are taking a long term, you need to focus only on JEE, so that you dont have board studies to do, in that case it is better to opt JEE advanced which covers almost every topic of JEE Main,by doing this you can have idea about both the levels of JEE, if you are preparing for JEE along with your board syllabus then its better to cover JEE Main. Hope this helps

Yes its a good strategy but take it as to cover almost all the topic lightly but the ones you are focusing should be in such a sense that you dont even skip a question from it. It should be like not even a single mark should go from that topic. 

Focus on the most important jee mains topics . On career 360 you will get the most important jee main topics . Solve lots of problems on these from Arihant books . 

Try to get the concepts clear from ncert and then try to solve Arihant . It should be enough . For chemistry ncert is more than enough. For maths again follow the same strategy.

In the Arihant books there will be portion for both mains and a portion for advanced. After trying the mains part you can also try out the advanced questions , after you are sure your concepts are clear.

They will help you in the mains exam too.

Try to practice within time limit , that's also an important thing