Hello khajanjoshi,
(a)
First, you need to decide if you want to have a dedicated object type for theses "identities", a bit of input to help you:
- Know that you cannot define multiple forms (RCDC) per object type and per action type (Create,Edit,View).
- Self service passwords reset works only with person object, so do you need this features?
- Only person object can log into the portal, so do they need to connect to the portal?
For starting to use RCDC, please see this page https://learn.microsoft.com/en-us/microsoft-identity-manager/reference/rcd-configuration-xml-reference
(b)
See UocIdentityPicker control of RCDC. You will be able to reference a normal user (person) on your external user object (person or new object type)
Best,
Sylvain