My advise to any new professional, though, is the same: know the craft, know the business, and gain initial experience under the thumb of a seasoned professional.
Absolutely. The questions about whether an opened film back will ruin a roll suggests to me at least that some more mileage in becoming acquainted with the craft would be desirable before dipping one's toe into the professional realm.
I'm hoping that being a film-only wedding photographer will land me into a more laidback, artsy clientele.
An 'artsy' clientele will be attracted primarily by appealing work and maybe by a certain type of personality. I think you'll be hard-pressed to find anyone on this planet who prioritizes their wedding photog shooting film over more regular requirements like getting photos in a style they like, getting them within a reasonable timeframe, dealing with a professional who knows the drill of shooting an event like this, an overall smooth transaction, a social connection / the feeling the photog understands what the couple wants, etc.
If you search on this forum you'll find one or two recent threads on questions along the lines of "which professionals on here still use film for their work". You'll find that the answers split into roughly two directions:
1: A very, very tiny number of members here who do shoot film and do so professionally. If memory serves, two or three of them. One is already posting in this thread. I'd take his advice on at least bringing a digital backup (or rather, using film as a bonus/add-on) very seriously indeed.
2: A vast majority who feels (and sometimes, damn well
knows) that shooting film, charming as it may seem, is from a business point of view a dubious and in many lines of work probably downright stupid thing to do in this day and age. Wedding photography may be one of the few niches where there might be some appeal to the film proposition, but I don't think it'll sell as such - it will only work as part of a package of an overall decent/high-quality and appealing proposition (not just photographically so; see earlier comments).
Of course, many successful entrepreneurs will argue that they've been told that their ideas were stupid when they just started out, and look where it got them. But remember that there's a vast number of people, outnumbering the successful entrepreneurs by a massive landslide, who have learned some painful lessons because they didn't listen. Which is to say: by all means, give it a go, but don't give up your day job, and be very cautious of what risks you're taking. I've seen (and sometimes advised and evaluated/judged, professionally) my share of nascent entrepreneurs, and to be frank, your idea is one that would have garnered a vote of sympathy and not much else.
Sorry about the confrontational message, but as said, it would be odd if nobody would highlight the obvious problems with your idea.
Now, please carry on and explore the idea further, especially the aspect of how shooting film might (or might not) add to a sensible value proposition within a specific niche of wedding photography.