Sizes for that stuff depends on what kind of character I'm playing. Most of my characters use Boobswell to hit at least a G-cup, though my merc got the Sneezing Tits while doing the amazon Treatment and ended up with MM-cups.
I usually go for a random boob size at character creation and just see how they grow as I play. I wish there was some option like the Honeypot perk that didn't involve lactating, because I like BE and it'd be cool to have a character whose boobs were slowly but constantly swelling.
Dick size is usually a struggle between wanting a ridiculous-sized dong and still being able to fit it in people, though I always pack on some extra girth. CoC got me into that. My tech spec keeps her dicks at 11" by 3", because much bigger than that and she can't fit into Anno's ass, and she has no balls. My amazon merc rocks a 12" by 4" horsecock, with two 4" balls. I still need to get a second dick for my smuggler, so she can have one that can fit in anyone and one that's a third leg, and she's got three giant balls because I read there was some Kally stuff you can only get with 12" testicles.
As for ass and hips, that varies on how I see the character. Most of my characters get at least some of both, but my smuggler's curvy as hell, my merc and techie not as much. Everything else people are listing - hair, ears, tails - is different on every character, based on what I want to play. Still need to make my merc into a catgirl instead of a cowgirl, though, seems like it'll be fun to play that.