I like all pulls. Find something that comes in multiple sizes. A 6 inch is nice on all upper doors.

Drawers? Roughly a third of the drawer width works nicely. so a 12 inch is very nice on a 34.5 inch drawer. A nine inch drawer? 3 inches ....

Don't be neurotic about it, as close enough is good enough. Make a list of all the lower drawers Count lower DOORS as an upper. : )

It depends what your style is. And yes you can do knobs on doors, and pulls on drawers. Same finish.

Make sure the knobs and pulls are comfortable in the hand as well as aesthetically pleasing.

I prefer pulls to knobs. I used the same size pulls on all my cabinets and they work just fine, even the 36" drawers with heavy pots.

You can mix pulls and knobs. As for size I look for pulls that come in different sizes so that I can adjust with drawer width. In first picture I have a pantry which is 35” wide - with 9” pulls vs the coffee station which is 25” wide has 7” pulls. The 7” is also on upper cabinets. The cabinet over the refrigerator is 14” tall so I used knobs. These came from Top Knob so I order the larger pull and knob as sample at $5.00 each to check size. Then order the balance from Build.com who had a better price at the time.