My only problem with Katy is that she requires the pubic styler. That's not something I care to spend points on.
A little-known fact: If you haven't got the pubic styler, it's not the end of the world. Instead of the precise style specified in the character file, you'll get one of the "basic", four styles. See
the customization thread for details. I think any custom colour will still work, but I'm not 100% on that.
So: worst case scenario, her pubes don't look exactly as her creator intended.
One problem I have with the requirements, too, is I don't know which characters have which hairstyle. So I don't know who I need to get to make the character work.
On the add-ons shop page for the custom character, click on the "Hair: (whatever)" text in the "requirements" section. It's a link, and will search the shop to tell you which character(s) that hair comes with. Alternatively,
this thread has a handy-dandy list (which is a little out of date now - off the top of my head, it's missing starlet/bella).
Also, even if you don't have the hair, you can either use the hair styler add-on (if you have it) or edit the XML directly (if you don't) to change the character to use a hair you do have.