Hi @sindhujasrivastava
The best way to achieve your destination, is to use Azure AD B2C for authentication and publish your app through Azure AD B2C, to your customers, the reason I recommend that is because maybe not all of your customers have Azure AD for B2B authentication, so If you enable other kinds of authentication protocols for example if your customers use G-suite, or other ID Providers, they should be able to sign-in to your app with their managed credentials, and for additional security you would probably want to consider MFA, but that option was only recently announced at Ignite for Azure AD B2C so that's feature that is coming soon.
Getting Started with Azure AD B2C
Create your Azure AD B2C Tenant
But to answer your questions:
1. If you provide as Sign-in/Sign-Up page to your customers after setting up your APP with Azure AD B2C they can sign-in with their account and accept consent.
2. Yes your app needs to be added to enterprise applications at least in the tenant that you are going to publish the app from, whether it will be Azure AD or your Azure AD B2C tenant.
3. You need to submit a request with Microsoft if you want to publish your application through Azure AD Application Gallery, see documentation here: https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-app-gallery-listing
I would recommend you to use Azure AD B2C for your scenario.
Hope this gets you started, Good luck with your project.
Regards
Haflidi.
