I have never heard of roasted pork belly and the word “main,” so I had to check your profile. I noticed you’re in Australia; I’m in the northeast U.S. and I think our choices might be different here. I’m guessing your entree is like our appetizer course, since you mention a tomato/feta tart and the main is the large plate (protein, starch, vegetable, garnish), which I’d call the entree course.
Along with the pork belly, I also haven’t seen duck offered. (Invited to 10 weddings in a 3 year period). It seemed as though the most popular choices, in our region, are chicken, beef/filet, seafood, and vegetarian. More than half the weddings we’ve attended offer 2 entrees plus vegetarian, with some offering 3 plus veg. It’s becoming popular to offer a duet large plate; the one I’ve most frequently seen is a beef/chicken combo.
Both of my daughters chose vegetarian soup and salad, as their 1st two courses. Both offered a vegetarian entree (with the 1st to marry, over 11% (27) of the guests chose it; with the 2nd it was over 13%). The one with the smaller wedding (2nd), with all the catering coming into the venue from offsite offered a chicken/filet duet. There was a pricey upcharge, to offer another entree, due to transporting, so they just chose the duet and vegetarian. The other (1st) had her wedding at full-service hotel and offered 2 duets; the chicken/scallops was chosen by about 1/3 of the non-vegetarian guests, and beef/crabcake by the other 2/3rds. (None of the guests had a shellfish allergy).
I always request the vegetarian entree. I know that salmon is sometimes an iffy choce, as some people (including my mother), think it’s too strong. In our area, there are always some guests who don’t eat red meat. At the daughter’s wedding with the chicken/beef duet, two guests asked for a double chicken. instead.
I guess I haven’t been much of a help. I think it’s one of those “know your crowd” type of things and what’s popular, in your social circle. Good luck with planning.
P.S. I agree with differences in regional hosting. In the northeast we offer a large amount of food, during the cocktail hour, and at least 4 served courses. Later in the evening there’s some type of additional food, such as a dessert bar or mini sandwiches. My family attended 2 other weddings in the U.S., which required an air flight, and the hosting was not as substantial.