Dear Sir,
As per Reverse Charge Mechanism Service receiver is liable to pay Service tax department, accordingly you need to register with Service tax department also need to file Service tax return, along with application St-1 you can submit request letter to Service tax superintendent to avid penalty for non filing of St-3, I suggest you to add all RCM service tax categories in ST-1 application to avoid multiple amendments in the same.
Please get in touch with Service tax practitioner near by to your location.