Personally I have no issue, and even enjoy mixed fixtures, but not in different color families. Your ORB is a warm finish and the nickel is cold. I mixed old gold with ORB and it flows wonderfully, but the nickel flusher stood out like an ugly thumb (IMO) so I changed that out quickly. So my answer, never with those two finishes. People love many things, which does make them work for their space, but not necessarily for everyone. If you are never going to sell...than don't worry, or if you don't mind changing them out...but if you can change it, I'd go with the same body of color (warm or cold) verses trying to make the two work together...cuz they really don't :(

I was asking recently about a hood and small pendants (older thread). My solution involves the symmetry of two small pendants working with the hood. I like high-hats for their unobtrusive lighting, but my personal taste is to have something decorative providing some light and some style at the same time. I say yes, do a pendant. It's hard to visualize your space, but from the description I'm thinking a long bar light over the peninsula, and the hood over the island.

The new one should have come with a different adapter.

I Agree with Chispa, placing a semi-flush at the center of the powder room will give you a great amount of light. These are some good options. the warda semi-flush comes in four finishes and three sizes https://www.douniahome.com/collections/semi-flush-mount-ceiling-lights this is also a nice geometric option it comes in four finishes and three sizes https://www.douniahome.com/collections/semi-flush-mount-ceiling-lights/products/ula-semi-flush-mount-light