We bought most of the essentials already. We have our nursery done (mainly because I wanted DHs help in painting and assembling furniture.... he's gone a lot with his new command right now) and we have the stroller and carseat (my mom bought for us... she wants us to be ready! ) Other than that, I've bought some cute gender neutral outfits here and there and some books. Nothing major.
Unless you are the kind of person who does get sad looking at a nursery already done, I don't see the harm in getting the essentials done and out of the way in case something comes up quickly. I'm the type of person who likes to be prepared though. It's a completely personal choice, and neither side is wrong
