Peter,
Good to hear from you, and hope all is well.
Most social networks do not let you create an application with just an IP address. They need a domain to use as that's what users will be using. There are ways around this for development, but I'd recommend getting a domain name (even a free one with something like
free TK domain
just to have something to test with. You can setup and test with the temporary domain and then move all the apps to the final domain when you have it.
We've never used Membership Pro, so I can't guarantee everything will work fine. As always though, JFBConnect creates 100% standard Joomla users. If they register with a social network, you absolutely should be able to funnel them through a subscription page to purchase a membership. JFBConnect shouldn't prevent or cause problems with that.
I hope that helps, but if you need anything else, just let us know.
Thanks,
Alex