HeyshubhamguptaWell, you have so many questions, but as most of them have been covered by
yashikaaggarwal, I will try to answer the one regarding "whether you should go for CAT or GMAT?".
To decide it, you need to consider the below mentioned factors:
Work experience : In case of GMAT, you need to have work experience to apply for B-schools; but in case of CAT, IIMs prefer fresh graduates or in case of experience - the lesser, the better. Search about
Application rating(AR) system for IIMs on Google.
B-Schools & Specializations : You need to decide the specialization or major you want to do, and hence the schools & locations e.g. IIM B is best for MBA-Consulting in India.
Applications and SOPs : You do not need applications or SOPs or stories or LORs when you apply with CAT, but in case of GMAT it is mandatory.
Fees and Scholarships : For an MBA program with IIMs via CAT the Fees is pretty much below 22 lacs for all the schools and you do not get scholarships, but when you apply with GMAT(to schools abroad),the fee is more on higher side. Good thing is some B-schools are very generous to provide scholarships on the basis of your application/profile.
Regarding Quant, the level of difficulty is almost same except there are few more chapters that are covered in CAT, but in case of GMAT the questions tend towards logic more than theories or utilities.
I, myself am a 92 percentiler in CAT Quant but I still am struggling to get a Q50 in GMAT mocks. So, GMAT Quant is not easy, rather it is more logical.
Since you will be graduating next year, you have sufficient time to figure out what do you want from your MBA. You can appear for CAT and get into the prestigious IIMs, or if you want to go with GMAT you can go for YLP program of ISB.
Best wishes.