Colleges in Pilani

According to me, Nirma is the best among these three institutes in terms of both placements and infrastructure.
The average placement package of Nirma university is 8.1 lakhs where as that of Welingkar is 3.2 lakhs. So, there is huge difference between the two colleges.
I do not have exact information about the average placement package of BITS but it is almost same as Welingkar.
So, on the basis of the placement packages offered I would rank Nirma University above these two educational institutions.

BITS Pilani has very high brand value. It is accepted as a college equivalent to IITs in India and abroad. Therefore, graduation at BITS Pilani campus will be a better option.

FMS IS ONE OF THE BEST ITS GREAT U JUST WANT TO GOOD PERCENTILE IN ENTRANCE ATLIST MORE THAN 95% GOOD LUCK

PSG, Coimbatore is a better option if you get admission in it. Fee structure is somewhat higher in comparison to other colleges but it is worth it. It has good placement records till now.

No BITS pilani is not accepting XAT scores.In Rajasthan only Array alliance and VGU Jaipur accepting XAT score .

All disciplines are allowed.

Your Chances are low because of your low CAT percentile and there is no reservation in BITS.

Yes, you can apply to the JEE Mains but you won't get admission to NITs or CFTIs based on your JEE Mains. Even your score card will not be released. If you qualify the criteria for JEE Advanced (top 1% and others) based on your Mains exam, you can give the JEE Advanced.
So, for you, the sole purpose of giving JEE Mains will be to get into IITs and not NITs.
You can apply for BITS Pilani too.