I'm happy you went with your instinct. Personally I don't like every finish to match and you'll find that you will never look at the rings around the can lights but you will either admire or hate your light fixtures depending on whether you go with what you like or with what you think it needs to be. I have different metal finishes in almost every room in my house and my kitchen actually has 3 different ones and I love it. The panic you are feeling is just the culmination of months and months of decisions -- you are literally worn out. It's also the anticipation of every single decision coming together for the final "reveal" that you'll have soon. Take deep breaths and keep saying "this too shall pass."

I would go larger if you are set on two pendants, otherwise they'll look tiny over the island. One way to to test the look is to make paper cutouts of different sizes and test them over where your island will be. Restoration Hardware's Benson pendants are similar, and Kichler Lighting makes versions as well. Here is a link to your pendants: VC Yoke Pendants

You want your pendants appropriately spaced over the island since that's the space they're providing task lighting for. While it would be nice if that perfectly centered them with the room, window, and opening, that's not nearly as important since the only time they would ever look perfectly lined up if they were centered is if you were standing totally square to them. The vast majority of the time you'll be looking at the kitchen from an angle and they wouldn't look aligned anyway. Are you thinking of using the pendants and the sconce together? I don't see them working harmoniously in one space.

Make sure you have 450 lumens of light at the counter for task lighting from cans that are in front of you when you're standing at the island so your body doesn't create a shadow. Then pick anything you like for ambient lighting. Or something colorful without lights.. . .I'd wait until everything else is in there.