Do i need to fill itr?

As per Income Tax Act, it is mandatory to file income tax returns if Gross Total Income is above basic exemption limit.

So ideally, you are liable to file your income tax returns for period 2017-18

It is always advisable to file your income tax return. 

Yes, should file the ITR, as you have gotten advances, its better to prepare the financials and file the ITR

Yes, your friend might go for presumptive income scheme u/s 44AD, 44ADA, 44AE. ITR IV depending upon the nature of the business.