Gst liability

Hi 

I am not sure if my income in this financial year will cross Rs 20 Lakh. 

Q1. Will I still invoice my clients with GST invoice and pay GST ?

Q2. What happens if my services are over before income crosses Rs 20 Lakhs ?

Q3. Will I get a refund later for ZERO Liability of GST ? 

Q4, I would have claimed GST from my clients, so in case of any refund, would I still have to repay the GST to my clients ? 

Q5. For April I did not claim GST. Can I claim GST in case I have no choice but to pay GST now.