My opinion only, and I'm not a professional decorator...I prefer the look of two lights versus three in general and especially because of your hood. If you like the look of the smaller one better, use that one. I have seen quite a variety in terms of size of pendants in relation to island size, so anything goes. Although I'm sure there is probably a "rule of thumb". But as long as you like the way it looks...nothing else really matters.

I like that mock-up. That looks great Rebunky. I just made a "Globe Pendant" IdeaBook on Houzz hoping to find an island Erica's size & specific globe pendants sizes. So frustrating, as either the island size wasn't listed or the pendant size wasn't listed. While I was doing that, you made that great mock-up. I really like the two pics of the black island kitchen you posted earlier and the mock-up looks very much like that size & spacing. The outer pendants might be able to move just a tiny bit closer (a smidge) to the edge of the counter. edit: based on the mock-up, 14" pendants?

If the fixture is hardwired, a wall switch is required by code. The wall switch can be left on and a secondary pull switch can be added.

There is no "size rule", but there are good principles for both proportion and for illumination. Some folks like "decorative" light fixtures, sometimes called chandeliers. Some folks, like me, don't like light fixture which call attention to themselves and attempt to dominate a space. Pendants can be large, complex and visually strong...or they can be small, simple and unobtrusive. Pendants can be clear and transparent, or they can be metallic and opaque. Thus, it's virtually impossible for anyone here to give you a definitive answer to your question, especially without seeing your house, the interior space and furnishings. If you are having trouble figuring out all of this, why don't you pay a designer for an hour's time and help you select pendants which will be workable and in good taste for the style of architecture of your house?