I just wanted get clarification on using CBConnect with CBsubs. If someone registers with social network credentials, will newcomers bypass the registration page (where they complete their contact info) and immediately go into the plan page and then payment?

No, they will immediately bypass registration and be logged in. You can set the registration redirect URL to be to the CBSubs plans page though where they can then select a subscription

If we need to collect other info that is not collected or synced with social networks, does that mean certain fields cannot be set up as "required" or does it simply ignore this parameter?

Any fields you do not or can not map from the social site will need to be completed at profile edit.

I suppose the only way to collect the info is after the fact with users editing their own profiles. Is that right?

Correct.

Will this affect anyone who does not use CBConnect to register or sign in?

No, CB Connect settings have no affect on those who register and/or login without it.

Not likely as only absolutely major social sites or login systems will be implemented to avoid over bloating the plugin. More niche sites should be implemented by yourself or others as needed. I am also avoiding oAuth 1.0 social sites as much as possible due to the complications with such implementations.