SOM-FM or FM-Thermo ?

I'm a fulltime working professional who is preparing for Gate XE for Mtech in Mechanical Design.

Im totally confused what subject combination to choose for Gate XE.

I have completed SOM & FM till now and half way through for BTA & Applied is still pending. I haven't even started with maths & apti yet. Considering the timeline should drop my prep with thermo & focus more on question solving, math & apti or should complete thermo & keep that as my back up option.

And I also want to know whether there will seat allotment restrictions based on the subjects chosen.

Also advice me on which subject combo to go for my preffered course.