GATE

You may check all details here:
http://www.gate.iisc.ernet.in/?page_id=130

Take some course's, online tests ,previous papers , tutor's etcs.

start solving mental ability questions and also take out notes of EC

its upto you dear.
people preparing for GATE from 5th sem. as you will have 2 years and you will prepared well for Final year GATE exam. so Start preparing for it.

Aakash, Allen, Rao, FIIT.

If you have done textile engineering then PG from NIFT will be a better optiin because NIFT is related to designing. M.tech through GATE also have options for pursuing course related to designing but. there are very few colleges and courses available in this case. Hence go for NIFT.

in my opinion, coaching is not at all compulsory for GATE. However if you want, you can join a coaching. GATE exam checks your aptitude in engineering subject.So, you must have your basics clear. keep referring to the standard books, and practice a lot of questions.