Congratulations on start EASY with your LO! It will be well worth it--I can attest to that!
In regards to the sleeping past three hours...it is best to keep the feedings every 2.5-3 hours. This helps establish a routine. Just the same as AM wake up and bed time. However, if you find your LO is hungry, by all means feed her. Sometimes you can "buy" a little bit of time with a paci, if you want to go that route--just to try to push the feeding back a bit.
The dream feed is something which is really helpful in topping up your LO. It is typically done around 10:00-11:00pm (around the same time every night) If you too go to bed when your DD does, then I would say it would be beneficial for you to get up at 10:30 or so, rather than 2, 3, 4 etc
I found with the DF,that it did not work immediately, but after about 7 or so days, I saw a difference in the nightwakings. Every LO is different of course, maybe yours will catch on right away!