Sincerely, DogFiesta.com is fine. If you're looking for something that can work just for dogs … but for ALL aspects of dogs … "Fiesta" is vague enough to cover anything, but it's fun and familiar to an English-speaking American audience: which is important And "dog" is precisely the word you want to point; so having it in the domain name is crucial. If you want to opt for an alternative, I suggest that the second word begin with an "s". In that way, the domain will contain "dog" and "dogs" and will benefit from both traffic flows. Maybe DogSource. But the second word must be a common word, something catchy and unforgettable. DogSource has a disadvantage because "source" is a fairly abstract term, difficult to visualize. DogFiesta, on the other hand, is screaming for a logo that will help people remember your website. That logo, without a doubt, must be the image of a real dog wearing one of those conical party hats.
PS Stay with the .com. There are many options available in this extension. As DogFiesta has already registered, I would not continue searching unless I wanted to increase your budget. If you had a bigger budget and time to spare, you could look for a different domain of the .com variety with a second strong word that starts with "s", a word that is immediately memorable as "party."