The spacing of the pendants sounds pretty good. I'm skeptical that the little 4" models will look proportionate to the island, or cast enough light to work by, but that's probably not critical at this stage; it sounds like your builder just wants to install the rough wiring and ceiling boxes. As for can placement, many builders prefer to put cans out over the aisle spaces. While this does make exact fixture placement more forgiving, it also makes it inevitable that your own body will cast a shadow over the area of counter where you're working. I'm of the 'directly over the counter edge' school of thought. This prevents such shadows, but also places noticable splashes of light across the upper cabinets, which makes it necessary to place these cans especially carefully. With 9' ceilings I'd probably use 5" or 6" cans, shoot for about 4' spacing over the counter edges, and plan to use 75 watt, 40-degree floods.

My mom, who's only 5'2" now (used to be about 5'8" before arthritis and osteoporosis took hold) wanted to hang her chandelier only about 25" from the table. I laughed when I saw the handyman hanging it because I could see the bulbs -- and it was an up light! I finally persuaded her to hang it higher, mostly because she would've hit her head on it if she stumbled when walking by the table (small table...). 32"-36" seems about right.

I already have one...since it is not too bright, so far I have not needed it there! I'm a dimmer junkie...it's a rare room in my house that doesn't have one. I have them in the bathrooms too, since I can't face bright light until well into my first cup of coffee.

Given the size of your island, I don't think 3 pendants would be too many. I've also seen photos of large islands with only two pendants that are beautiful. Think about where the pendants would hang should you choose two or three and stand at the island. Do the pendants obscure your view of a focal point in your room? What about your line of sight into another space? I'm renovating my kitchen and downsizing my island to 5'. I'm considering an 11" pendant and will use two because I am able to place the pendants so that the distance between the pendants and the distance from the edge of the counter to the pendants is almost equal to the size of the pendants. As long as the scale of the pendants feels appropriate to the space, I'm sure whatever you choose will be beautiful because you made your choice based on what makes you happy. So take the advice of your electrician, and me, with a grain of salt and choose joy. Would love to see the end product.