You don't have to. You can mix metals. Just depends, but personally I would stay with the same tone or similar.

Because of your appliance color, changing the color of the pulls doesn't really make sense - stick with the stainless - or brushed nickel.

I think that the only thing in that mix of metals that you need to consider when it comes to your hardware is your faucet and your light fixtures (which you don't mention). So in my opinion your sink and appliances act as neutrals. After all, nobody has an ORB appliance or sink (or very few anyway) and yet plenty of kitchens have ORB hardware and look beautiful. If you look at Houzz photos with ORB you will find plenty that also have stainless (appliances in particular). And mixing metals is definitely trending, So in my opinion, I'd use ORB hardware without hesitation, provided that you (1) change the faucet to ORB, or (2) you have light fixtures that are ORB, or (3) you introduce ORB in accessories. I just wouldn't make your cabinet hardware the ONLY ORB in the room. I think ORB looks great with countertops and cabinets like yours, so if it were me I think I'd be finding a way for ORB hardware to work. It's a much warmer looking aesthetic than stainless and it aligns well with the rest of your colors.

Here is a good example where everything you mentioned is stainless, but there are ORB light fixtures and a large ORB clock. Therefore the ORB hardware looks fine.

SS sink and brushed nickle faucet.

You can absolutely use ORB hardware. I would be more concerned with matching your light fixtures, plumbing, and hardware versus the appliances and sink. Appliances and sink are neutrals, as someone else suggested.