If you're going to boil for 60 minutes, then you really don't get that much flavor out of bittering hops anyway.
So I don't know what the intended OG is for this batch, but a quick runthrough on beersmith with it as 1.070 got an IBU value of 32.6 for that AA% of Northern Brewer. I don't think that 2 IBUs is going to be that noticeable to you, so you should be able to throw the whole bag in (that is, if the OG is actually 1.070 or slightly higher).
In the future, I would recommend getting a free trial of Beersmith so that you can tweak your recipes in that. You can use it to determine what amounts of hops will give you the intended IBUs also.
If you have time, try to get the vanilla beans online. At grocery stores you can get them for like $7 for 1 bean, but online you can get them for something like $15 per pound.