Religious trust

Yes you can ,but it should not be against law or for illegal purpose.

Yes.  Without illegal purpose it may run with the same object.

I concur expert's opinion and advise.

So there is nothing against right to equality if we restrict other religion community from getting benefitted from ancillary business of trust

For better understanding treat the trust as a family or group as the contributions are received from one community person.  There is no question of spending amount within a family or community and equality claim can never step into such functions, once the internal rules state a specific purpose.  In many states, Govt are helping a specific caste group and directly funding those Society/Associations and there was never a question of inequality as the objective of formation is to help a particular community.