It depends on their height over the counter and the 'throw' (AKA 'spot size') they give.

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.

I like 3 too. 24 sounds really large. I'd prob do 18. you don't want the entire area above the island overtaken w/that umbrella-like fixture! 30-32" apart, and at least 12" from the edge. I'd say 18 is good or, you could do two of the 24"

Different goals come into play. Task lighting for when you work at the island counter requires 450+ lumens at the surface. The source should be placed so you don't shadow the work with your body. Ambient lighting is another objective. Recessed led cans on dimmers can do both. Pendants on dimmers or pendants and recessed lights can also do both. In addition, pendants can be decorative. Adequate task lighting is often missing in kitchen design.