I'm no designer but feel like I learned enough doing my own kitchen to get by.

Rules of thumb are to use no more than 3 metals (2 is prob safer) and keep metals in the same visual plane the same... faucets the same, lights the same, cabinets the same, door knobs the same

You can pair ORB with brushed or polished nickel, whichever you like better.

Here's mine with brushed nickel cabinet hardware, stainless faucets/range/hood (and coordinating "gunmetal" chairs), and ORB light fixture. There is also ORB+wood fixture over the island but none of the pictures I have on hand show it well. All of my new door handle are nickel, except the existing door had ORB and I didn't replace it so that's mismatched but it isn't really a big deal.

I'm not sure one has to limit to 2 or 3, but keeping, say, faucets the same, knobs the same, etc, is a good rule of thumb.

as for how many metals to mix-I'd say depends on the space, and how much it can be repeated..not neccessarily in metal itself, but with color of other material reminiscent of metal

I mixed the metals the most in master bath. I have there: polished nickel faucets and fixtures; antique brass drawer pulls and cabinet knobs; copper canopies and details on glass pendants that hang on black cords; and ORB door hardware. It sounds like a mess and I was deadly afraid when deciding to go for it; yet it looks pretty seamless, because:

-polished nickel plays well with the wall tile and countertop marble(main color very warm gray)

-ORB hardware repeats somewhat black pendant cords in its color

-since marble has rusty golden streaks in it, copper in pendants canopies picks it up

-the vanity is teak(lighter warmer brown) and the tile is shaped terracotta(darker warmer brown)..antique brass pulls I used on the vanity blend in with the vanity itself, and their shape repeats terracota shape.

Nobody knows how much courage I put into this mater bath lol; I'm not even sure they see how different finishes are; they just see a space they like a lot.

Repetition does wonders for harmony.

you most definitely can mix ORB with either brushed nickel or polished nickel

what I wouldn't do-I woudn't put polished nichel and brushed nickel together for example. Or i wouldn't pair nickel and chrome.

They should be different enough to mix them properly.

Oh, and of course I'm not a designer either. Just sharing my experience from a recent very long and big remodel.

Of course one becomes braver after one tries something. I never liked to match anything; and now inclined even less so:)