Although you could truly start with any Book 1 and bounce around between series, I personally think I’d start with Cookies and Curses first followed by Coffee and Calicos. The latter expands upon a story Joanie mentions to another character in Cookies. Coffee also introduces readers to Meredith, the main character of the Purrfect Travel Companion series. Foster Familiar takes place at the same place as Catastrophe on the Road, so you might recognize some characters depending on the order you read those in.