It will only look disjointed if (a) you have a tiny house, (b) it's all open and (c) you don't have the vision to pull it all together. If you don't have all three of those issues, you should be fine. The real trick is to be specific. If you're using chrome doorknobs, do so on the kitchen door, too, even though you have brass cupboard hardware. If you're doing some cupboards in the adjacent breakfast room, butler's pantry or anything open into a brass free area, get the cupboards styled a differently and choose hardware that works in both directions. If it's open and you have pendants over the island, try not to use metals and go for color instead. It's really not a big deal, if you don't go overboard.

If you spend some time looking on houzz.com you will see lots of projects with mixed metals. It really comes down to personal taste.

I am mixing metals all over my new build. I am ok with an eclectic look though, if you are a matchy matchy person it might bother you. As far as other people noticing 95% won't even bat an eye...you are hyper focused on it right now which is why you think it is a big deal. What kind of cabinet knobs does your best friend have, what metal are the door knobs in your mom's house, what type are the light fixtures in your neighbor's house? If you can answer all of those definitively, you will probably notice/be annoyed by different metals. I have salvaged brass hardware on some of my cabinets and I love it.

I am going to mix. All my door knobs are brushed steel and so is my faucet. I also have steel applicances. I will have oversize brass pulls for my cabinets. I can't afford the real thing though. I found some pulls at IKEA that I love the look/feel of and I will be spray painting them brass colour. I think the key to making mixed metals work is to repeat the elements. I will have some brass candlesticks and some other brass accents so that the pulls aren't the only brass element.