Welcome Beth! I was born and raised in San Diego and still live here so let me know if you need any suggestions. I've never heard of your wedding planner - are they local here? If not, I would probably use a local one as we have a lot of great ones.
If he isn't close with his dad and he isn't invited - I wouldn't see any reason to use the Jr - especially since you are doing informal invites. Are any of his extended family invited though that would be offended by not using it?