The first aircraft (400ER) is due to fly in July, apparently the testing program is around 90 cycles and 250 hours flying.
Number 2 off the line will actually be the first one to be delivered, which at this stage is November. Number 1 a/c will be the second a/c with a forecast delivery date of December.
I'm not too sure about the differences in fuel configuration beyond the fact that it will have some kind of additional auxiliary centre wing tank. As to whether it will feed into the current CWT as is the case with the stab tank config or otherwise I'm not sure.
I guess we'll find out more details closer to delivery date.