GST for turn over > 20lacs where income is from non-Indian clients

Hi, I have a web design agency in Rajkot, Gujarat. I have a question related to GST. I know that I don't need a GST number if my annual turn over is less than 20lacs. I'm expecting to reach turn over 20 lacs this year and here is my situation: 1. It is a proprietary firm. 2. I don't have GST number yet. I'm filing regular income tax returns and also pay advanced tax. 3. All my income is from out of India. Mainly from the US clients. 4. I get money using WireTransfer payment gateway that will accept funds in US$ from my client and I will get the funds in INR in company's current account. 5. I tried getting funds in US$ using transferwise and then in my bank account I converted $ to INR, but the overall transaction costed me a huge amount in terms of bank fees and conversion rates. As all the incoming funds are out of India, do I really need GST because as far as I know foreign companies are not supposed to pay the GST as it is Indian only tax. My clients won't pay me 18% additional GST. My questions are: 1. Do I need to get GST number if my revenue crosses 20lacs INR? 2. If I have to get do I have to pay GST and get a rimbursement or is there a way not to pay GST at all? 3. How do I prove that all my income is from out of India? As I mentioned, I get my funds via a payment gateway and thus I get it in INR only. 4. Any other advice on GST?