I tend to write a lot as a general rule, since I (like @MisterBoring) am one of those “write till I’m done” types, so my most recent apps are enormous because I’ve been really interested in the character’s until-now development. That’s just me, though, and it could easily just be a short story I write for myself without forcing anyone to read.
Anyway, that said, I think the app process should be similar to a mullet: short in the front, long in the back. Shorter app to get in and involved, with the idea that the character’s background info is a kind of living document, to a point, that can be fleshed out by making connections and associations either with other players or with ongoing plots.