Cats & Dogs SimGuru/Maxis-Sourced Info

Create-a-Pet (CAP)

There's a lot of SimsCamp info on CAP, including sample pets (puppies, robot and patchwork "fur", foxes...) and some of the UI. Here are some general places to start on that:
https://simsvip.com/2017/09/20/sims-4-cats-dogs-sims-camp-create-pet-screenshots-list/
http://simscommunity.info/2017/09/21/the-sims-4-cats-dogs-exclusive-screens-in-create-a-pet-by-simscampers/
https://simsvip.com/2017/10/08/sims-4-cats-dogs-sims-camp-create-pet-overview-list/

Blog post: Create The Most Unique Pets With Create A Pet

Trailer: https://www.youtube.com/watch?time_continue=2&v=WcpH2_JWeG0

Dogs come in two sizes: https://twitter.com/HyperboleGrant/status/899716700706353153 https://twitter.com/SimGuruLyndsay/status/899703986634186752
And puppies can be created in CAP too: https://twitter.com/SimGuruLyndsay/status/899693357240393730

There are breed catalogs to work from, e.g.... https://twitter.com/SimGuruJill/status/900241068897091584 https://twitter.com/SimGuruJill/status/900241258660020224
https://twitter.com/SimGuruDaniel/status/907288102464397312
The catalog includes long-haired breeds, including Lhasa Apsos, Yorkies, and Malteses (Maltese? who knows!):
https://twitter.com/SimGuruJM/status/907338062291656704
https://twitter.com/SimGuruDaniel/status/910630863494299648
Check out this thread for a breed list! KNOWN DOG BREEDS OF THE SIMS 4 CATS AND DOGS!! by @Roxygirl0987

Mixing breeds in CAP:
https://twitter.com/SimGuruDaniel/status/910913426565742592
If you tweak a breed... https://twitter.com/SimGuruDaniel/status/910913295770468352
https://twitter.com/SimGuruDaniel/status/910290897903874049
https://twitter.com/SimGuruDaniel/status/910642448304545792

There's some sample breed-mixing in Sims Community's YouTube video "The Sims 4 Cats & Dogs: 30 MINUTES of Create A Pet Gameplay".

Pets are paintable in CAP: https://twitter.com/HyperboleGrant/status/899691325276254213
https://twitter.com/HyperboleGrant/status/899692356227801089
https://twitter.com/HyperboleGrant/status/899717946938990594
https://twitter.com/SimGuruDaniel/status/900511331312320512
The system includes stencils & stamps: https://twitter.com/SimGuruDrake/status/900172599094681600 https://twitter.com/SimGuruJill/status/900244134098747392
But it’s just for pets: https://twitter.com/SimGuruLyndsay/status/899701811698835456
Is it just part choosing? Nope! https://twitter.com/SimGuruJill/status/900245405941628928

Clothing:
Are there pet outfit categories?
https://twitter.com/SimGuruDaniel/status/907309203831664640
(So... yes!)

Do cats also have costumes?
https://twitter.com/SimGuruDaniel/status/907294265566359552

Head to some SimGuru Twitter profiles to see examples of what you can do in CAP: https://twitter.com/SimGuruJM/status/900753535561678849 https://twitter.com/SimGuruNinja
https://twitter.com/SimGuruDaniel/status/900439033175654400
https://twitter.com/SimGuruNick

Example about how the pets fit in the household size:
https://twitter.com/SimGuruDrake/status/901282326738460672

Info from the CAP livestream, available to rewatch at https://go.twitch.tv/thesims:

• Animal eyes can be cross eyed.
  
• Dogs can have an underbite.
  
• Crop tail is an available option, not only on Manx cats.
  
• There are different available furs, not only limited to species choice.
  
• There are separate pet names for randomization.
  
• There’s a chow swatch that looks like a panda!
  
• There are three different poodles, with different hair.
  
• The left and right ears are not separately chosen but some dog ears are up/down combinations.
  
• Tails sometimes stop wagging in CAP but that’s so you can manipulate them; they do wag in game.
  
• If you leave paint on and change breed, you keep your paint job (but can remove it).
  
• Dogs don’t have different walk styles that you choose in CAP, but they do have emotional walks in live mode; if they did different walks they’d never have been able to finish the game (apparently that’s really development intensive!)
  
• Can’t have furrier ears than the body - not separately choosable.
  
• The dacshund (sp???) is there but has too-long legs because they couldn't do a third body size for them.
  
• There aren't costumes/clothes for kittens and puppies.
  
• You can set "natural" or "fixed" (neutered) in CAP with the three dots.
  
• There's a category for going-for-a-walk dog clothes.
  
• There are not three-legged animals because everything would need reanimating so would limit other development, but also because it's sad/depressing. (editorial comment from me: there seems to be a nudge against making things that are depressing in game, even if we wouldn't all find it depressing)