Honestly @jeanreidy, I really don't think the difference between satin and semi will make a noticeable difference as far as the depth of color, etc. It's really just the sheen. Ultimately, as I couldn't decide, I went with a 50/50 mix of satin and semi, and it looks great IMO.
It's great that you're doing three coats, just wait as long as possible before you place furniture down over the final coat. And be sure to abraid that second coat before the final round. Honestly, if you're intending to do a final coat well after those first two, you should consider doing two more, as it's easiest to do them back-to-back. (Then again, I'm not a professional installer!)
But we're very happy with the semi/satin mix and the floors are holding up well. Every time I see what I'm thinking is a scratch, it's just a smudge that gets wiped off. Sure, you can scratch this stuff -- finishes aren't made the way they used to, especially in CA where the formulations are highly regulated -- but if you take decent care, you should be very happy. Good luck.
Q