? Registration

You can run both business in One registration.

Yes you can use the same GSTIN. However, please ensure you are paying the due tax to govt and report the correct HSN

For retail business i already selected composition scheme for compliance ese
As per my knowledge composition scheme is not for allow for service provider.
pls correct me. if you have other clearification.

In view of notification No. 2/2019 – Central Tax (Rate) dated 07/03/2019, the Central Government, on the recommendations of the Council, has notified Composition Scheme for Service provider which can be opted from 01/04/2019. Previously, service providers are kept out of ambit of composition scheme u/s 10(1) of CGST Act.

This composition scheme can be availed up to turnover of Rs. 50 lakh.

would request you to go through the notification for details.