Larger stones tend to stay put whereas smaller ones are likely to shift when dry-laid (which sounds like what you want to do and with beautiful stones I always prefer dry laid.) If they have substantial thickness and can be packed fairly tightly they are more likely to stay put. Otherwise, you could try combining them with some larger stones, e.g. alternate areas of small stones with some large stones in a random pattern. If done well with the right mix of stones, this can be very attractive and stable.

Like Lisa, I'd be concerned that small stones would not stay in place. They're more likely to move when you step on them, or get kicked out of place.

I was trying to gather material for another short "flagstone" pathway using what flat fieldstone I have on my property and from scrounging, but mostly can come up with only fairly small stones (6-8 " diam). So I plan to buy some good large flagstone for the main stepping area and then use some of the smaller ones near edges and for lesser used zones where I want the stone look but doesn't need to be so stable and I want the kind of plantings between rocks thing. The concept is that you don't necessarily have to walk on the edges or utilize an area right up to its very edge, but the extra few inches of "floor" or pathway zone feels more spacious (and of course it won't HURT to step on the smaller stones). So as noted above, if you can look for commercially available stone that somehow complements your creek stones, you won't need to buy as much stone and could have a more stable heavy traffic/use zone and yet have a beautiful and unique look. You can find some photos of combinations for inspiration and guidance to decide what pattern might look best depending on the areas you are creating. I have seen some with smaller stones for edging, and some in which the smaller stones make a transition and lead into a larger- stone path, and so forth.