Tax dilemma/query

I am working in a Government agency.I have never filed income tax return as my income is less than 2.5 Lakhs per annum which is as stipend. I have not furnished my PAN Card details in the Govt office.Since April I am working in a private centre part time which is not declared to my Govt employer (sort of off the grid). In the private set up,I am paid as cheque and I have given my PAN number to them. I expect my private sector income to be less than 2.5 Lakhs. No TDS is collected from the private setup.

Now my queries are -

                   1.If my private income is less than 2.5 lakhs should I file income tax statement

                   2.How exactly is income tax depatment notified about my private income.Does it                                 automatically reach them?

                  3. Can anybody/IT inspectors see my private income if they query my pancard details in                       the income  tax network?

                   4.If by any chance my income is more than 2.5 lakhs,with TDS not collected, will I get                       a notice from IT Dept for  filing returns?

Sorry for the long question. Hope you all get what I am trying to convey.

                                                                                                                  Thank You