Private complaint

To my knowledge, a person can either go for filing a complaint u/s 420 of IPC or Section 138 of NI Act since both the complaints are falling under the purview of criminal laws.

Simulteneous proceedings wont help to serve the cause but only multiply the time limit.

It is always advisable to go for 138 NI Act since it has got comparitively speedy disposal than U/S 420 of IPC.

Very innovative idea to club Sec.420 IPC with Sec.138 of NI Act.  But if it is filed with an intention to escape the obligation to file within the limitation period meant for Sec.138, judge may catch your intention.  The test is, if it is filed within the limitation meant for Sec.138, then he will accept Sec.420 also.  If it is filed beyond the limitation period meant for Sec.138, he will understand that you are clubbing Sec.420 in order to escape your obligation to file within time limitation means for Sec.138. 

Yes. Private complaint can be made for Sec.138.

The best way is present the cheque again and get another Cheque return memo from bank, and this time follow the procedure correctly.

in a recent judgment., the apex court of india has ruled those cases being distinct in ingredients can go seperately.

420 can be lodge at Police station, and if Police co-operate, recovery is the fastest.. 

But very few P.S. Helps, They just avoid register 420 and send for 138 ni in court.