About presumptive taxation

Hi Fellas,

My wife and I export professional services in the Mental Health industry outside India while our permanent stay is in India. My questions are

1. can we claim 50% of expenses without keeping books updated under "PRESUMPTIVE TAXATION SCHEME"? 
2. Do we need to register ourselves for GST as the income might increase beyond 20 lacs per annum? I know that GST for export services will be zero but do we need to get GST registration?
3. How can we save more money and invest the income that can be tax-free?
4. Which Section of presumptive taxation applies to us? is it 44AD or 44ADA?
5. Should we create an entity and do business through that channel or we can save more individually?

Please share your expertise as it would be helpful so that we can make informed decisions about our finances. 

I appreciate you all who are reading and replying to this message.

Thank you.