I’m Irish, and I’ve been to mostly Catholic Church weddings. The only tradition that I’m aware of is don’t wear white.like so many other Irish posters, that dress would be perfectly acceptable. I don’t think I know anyone who would worry about the exposed shoulders in church. That’s something that most of us only experience when going sightseeing in Rome for example.
It is very relaxed in Irish churches around that sort of thing. weddings tend to be very dressed up - and I wouldn’t worry about the style or colour of this dress in the slightest.
I would go as far as saying there is no difference in type of clothes acceptable at a secular wedding to a church wedding in Ireland. If someone turned up with an arse-revealing outfit, they would be raising eyebrows at both! This dress would not be an issue at all.
Just to add, now that I’ve read all of the OPs responses, I think the colour is perfect, you can wear whatever colour you want (apart from all white) and it sounds like it suits you. Don’t worry about it at all.