How well do they pay?

Sorry I didn't respond earlier. You can set your rate however you want, however, your toptal guy will have to think it's credible.

I believe it pays way more than elance / odesk (however, I didn't really try hard there because prices are so low it would have barely sustained me) but my rate is still way below a good consultant rate of say 1k$ per day.

But it's good enough to live well even in an expensive city such as Luxembourg.

Just mind it's an investment so you should be good at what you're doing and have a few spare days spread throughout the next weeks in order to jump through all their coding / interview hoops.