Advice seeked.

1. Is it necessary to have promisory note or only cheque is sufficient 

The cheques are valid for 6 months,  and Promissory Note can be of any duration.  The promissor note will strenghthen your claim for  repayment of laon. You must get a promissory note from him as a better security. 

2. If promisory note is necessary is it required to be printed on a stamp paper. If yes what value of stamp paper is required ;

There is usually availble with stam paper vendors the non judicail paper- in hindi it is called; HUNDI .However you can print or write on a paper and start the wording as "on demand i promise to pay to....such and suhch amont and give full details of transaction. 

Banks even make witnesses to sign the DP note .

3. I dont have transaction reference to claim

That is secondry part. If asked you need to show that where from you have the money ;savings from your income , sold any thing, etc. 

4 lac, only 50k i have done a bank transfer. will the case have grounds at court?

You must make a DP note for that to show that you paid the cash as well as transferred the money by transaction dated....

Secure your money properly.

Don"t do what u are thinking. send him a notice under section 138 NI Act ..file a case...since your case dates will take months...ask your friend to give money within the case time and settle the case and later withdraw the case....  if your friend is true friend he will pay u