Building my collection: I try to focus on only buying new (either new to me or newly published) books if they cover a cuisine or region that I'm not already well-saturated with. So for Italian, as much as I love it and have tons of books, these days I'll only buy new ones if they focus on a specific region or style of Italian cooking. Otherwise I'm still a sucker for bargain bins and used bookstore finds, especially for older books that might have hidden gems in them.
And I am old-fashioned in that I don't like Kindle or e-books for cooking. General fiction and non-fiction reading, yes. But cookbooks, like art books, I still prefer physical copies and doubt that is going to change any time soon.
Maintaining: I keep my most-often used and new books I'm eager to explore in one of two book shelves right in my kitchen. Some of these are indexed, some are just so frequently used by me that I just like being able to quickly thumb-through them and search through while planning meals. The rest are stored in my pantry, which I did have re-designed a few years ago to include a one-wall bookshelf. That's definitely helped a lot with my storage issues! And I do enjoy member indexing as I have the time for it as I find it definitely helps me become mor familiar with books I have had sitting around unused for too long.
Culling: I'm loathe to get rid of cookbooks unless I've had nothing but bad results with the recipes I've tried from one. That's happened with a few "celebrity chef" books I've bought through the years. I'm thinking about culling a lot of my old magazines except for some specialty ones, like some Italian cooking magazines. I already get rid of my Food & Wine magazines once the annual cookbooks are released, and will probably dispose of my Food Network, Gourmet, and others as long as the recipes are mostly/all made available online (or I've copied out the ones I actually want).