Yup, we'd do that without any issue using the "Automatically link users by email" setting.
User clicks either button > email already registered, account linking happens automatically > user is logged in with one click
No, we wouldn't support that. JFBConnect/JLinked supports the built-in multiprofile system of JomSocial, but does not support JSPT.
User clicks ether button > email not found, diverted straight to JSPT Select profile type screen > Selects profile type > sent to JSocial complete profile stage 2 where information is prepopulated from FB or linkedin > user checks and changes any information necessary and completes registration.
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