I like gellchom's suggestions about breaking down the parts. I think that's great advice for clarifying your thoughts, no matter what the concerns are--it's just a thought experiment, after all, you don't ever have to tell anyone which list they ended up on.
After you make a list of the key people you'd like to attend, in theory, I would sit down with them and go over the ceremony, and see how they really feel when it's put to them directly as something tangible, not abstract. I'm pretty open-minded about other religions but I could imagine some things I would be very uncomfortable witnessing--let's say it was a Betazoid wedding where everyone was supposed to be naked, for example.
Even if they said non-Betazoid guests had the option of keeping their clothes on, I honestly think I would be too uncomfortable with the HC and various Betazoid guests being naked around me, to focus on the ceremony in the proper spirit. I would appreciate this being explained to me in advance and being assured that it was totally cool if I just wanted to attend the reception, and skip the ceremony, no hard feelings whatsoever.
I realize it's harder to have that discussion if someone is going to jump to "wrong" and "offensive" right away. However, for someone in the "inner circle" of family (for me, parents, siblings, grandparents plus SOs) I would rather have that conversation, where I make it clear they're welcome and then have them actively opt-out if they prefer, than assume in my own head which way they'll go and possibly cause deep hurt and disappointment at being excluded.
Also, I don't think that "family" should always go above "friends." I know a lot of people who are closer to their friends than to their family. It's just that in this case, it seems more clear which friends would appreciate the ceremony and which wouldn't; while the family is more ambiguous, so they need special attention.