I love the chocolate pyramid! At our wedding, we had old vintage glass bowls full of retro sweets. I think people like something sweet to nibble on later in the evening.
The Artisan favours are sweet, but I prefer the pyramid.
You do not need entertainment! It's a wedding, not a ... well ... I don't know. I always think it's a bit silly when people have magicians, wandering minstrels, dancers, etc. at their weddings and try and make a spectacle of it all. A band is plenty.
For the nieces, I'd prefer mismatched dresses too. But if there's only one thing you're going to concede on, I suppose for me this would be it. The Debenham's dress is nice. Not necessarily my cup of tea, but it's pretty and certainly not objectionable in any way.
If it's possible for you to get your own way about everything, however, then go with your original mismatched Cath Kidston idea.