Remittance of gst to govt. account

We are registered under Religiious Trust and collecting GST for renting Auditorium. the questions are..

1. waht is the due date for remittance of GST collected into Govt. accounts.

2. For offline remittance it is lerant that there is limit of Rs. 10000/- per chelan. How we can remit larger amounts through a single chelan by offline.

3. We are collecting GST only for Service. Whether we have to file monthly or trimonthly  return and when it is due.

Thanks in advance