Dear Divya,
While implementing LSO for my client I had also same query, but fortunately they didn't have B2C scenerios i.e. no external learners.
Are you implementing this for any Educational industry ?
You may go ahead with SAP Web channel Experience Management solution meant for e-commerce of B2C scenerios.
Please check the thread for overview of SAPWeb Channel Experience Management http://www.slideshare.net/collsdad/solution-brief-sap-web-channel-experience-management
Answering to your queries directly,
1.Same scenerios of Ext Candidates in E-Rec- Admin can forward a link with which they can register.
2. & 3. Please go through SAP documentation for under component PE-LSX.
As an work around which we did for a support project you can create External Persons (object type H) for them and use infotype 1032 subtype SAP to store their SAP login id. You will have to come up with a process to activate/change/delimit these objects.
Once you have the process setup to provide these people access to the portal and they exist in the system as H objects, you can use the Badi LSO_LEARNR to map the object id (reading 1032 based on SAP login id) to the learner id.
You need to follow up with your EP/ABAPer along with your functional knowledge on xLSO.
All the Best !!!
Regards,
Niladri