Whatever you decide, EBM or Formual, give the bottle ASAP. We tried to get our lo to take a bottle for a month, she just won't take it. I started offering it at 11 weeks. She's now 18 weeks old and I'm waiting for the haberman soft feeder and the finger feeder, these are our last hopes for her to be able to eat while I'm away. Until she starts solids I guess.
But personally I would stick with EBM as you lose whatever you supplement in formula. It depends on how long you are hoping to nurse. The more formula she gets the less milk you'll make and in the first 6-10 weeks is when your supply is basically set. I wouldn't offer formula before then if you are worried about it.
Also I read that the iron in formula can effect you lo's ability to absorb the iron in your milk, just a thought. Go to Kellymom.com for more info on stuff like this.
Good luck and congrats on your new bundle.
~Patty