1. Do you also save the zipped files?
Nope. I unzip ASAP and then delete, delete, delete.
2. Do you typically use each kit to make just one page or multiple uses?
Just once, usually, although there are always exceptions like a very themed kit. I delete every template once I've used it once.
3. Do you remove kits from your 'database' once they've been used as many times as preferred?
I use a kit once, and I delete the kit afterwards about 80% of the time.
4. How do you handle kits that are retired/from retired designers?
I move that designer's folder into a "Retired" kit on my EHD. I don't really need to do that (and sometimes have to move it back when a designer "un-retires") but it just makes me feel better.