Well, on CD3, it's too soon to tell which will be dominant, because it's so early in the cycle. Once the dominant one(s) take over, the others will quit developing.
I might not be much help here, but I'll try! I haven't done IUI yet, but I've done Clomid with HCG injections, and this cycle was with Femara. I know that the earlier the u/s, the more follicles you're likely to have. For me, there is usually one (one time there was two) dominant follicles that take over later in the cycle. But the number that you're starting with is great!
Last year when i was trying to get preg with my son they had me on clomid they were watching for the follicles and they want at least one or two but they have to be a certin size before they can contain an egg and then it only takes one were the ones they saw on you all dominant? if so that is great and if they all release an egg Uh-Oh!!!: ) Good luck and baby dust.