So, good news: I don't think it's too soon to be reading the book. I ripped the first chapter apart (which was no surprise-- the first few chapters always need a ton of revision), and felt like I knew what I was doing and what the chapter needs to be stronger.
Not really "bad" news-- more like "hmmmm" news: I'm having a difference of opinion with myself about the sequence of the revision steps. My original idea was that I'd read and make notes on the entire draft, then make those changes in the Scrivener file. Now that I've made notes all over chapter one, however, I'm wanting to go edit the chapter now, while my idea of what needs to be done is fresh in my mind. So I think that's what I'm going to do-- for now, at least.