Beta testers technically already have their keys I believe, so regardless they will be the first to download. Impulse should be fine since it's a downloading client; basically that's all people use it for and it's what it does.
Even if they gave you an estimate of preorders, it'd be near impossible for them to tell you how many will be downloading and at what times. As for the keys, I think they already said they'll be doing it manually through a program. Considering how a similar program from a company a mate of mine works at operates, I'd assume they would charge a preorder and once it goes through activate the serial and send it out via email.
Supposedly if you signed up with the same email, it'll activate in impulse without needing you to wait for the key and then enter it. I know I'm not a Stardock employee or anything but from the bits said that's what I have gotten.
