FIlling tax as freelancer

Hello everyone,

I need some help filling my taxes for previous FY and current FY
This is my first time filling taxes, I work as a freelancer offering IT services worldwide and have no salaried income here in India
I am receiving payments from individual clients and companies through PayPal & directly in my bank account
I have few questions,

1. Which ITR form should I file? ITR-1 or ITR-3? 
Some people are saying I can show it as income from other sources in ITR-1 while some are suggesting ITR-3 as it is a professional income

2. Other than PayPal, I receive money in my bank account through money transfer services like transferwise, worldremit etc In which section should I declare this income?

3. Do I need to register for GST in this case and issue any invoices to my clients? My current turnover is well below 20 lakhs

4. Do you suggest other payment methods for receiving money from overseas clients, if it makes filling taxes easier in future?

Any help will be appreciated

Thank You!