Oh, yeah, made my brain hurt too! I'd done fingerless mitts and realized:figureditout: a chihuahua sweater would need two openings for legs instead of just one for a thumb, thus was born the Mutt Mitt. I don't know if you could use the same method for a larger dog, but I just figured out how many stitches for the sweater to go around the dog, started with ribbing, then continued in stockinette after the ribbed neck and did two openings. I worked flat on the front and back sections then joined them to go back to working in the round. On one I used short rows to make the back longer. One got ribbing round the leg openings. Ribbing at the bottom helps keep it in place and prevent curling. I look forward to seeing what you end up doing.
No, a dog sweater shouldn't be too ambitious, just pick one that looks doable. If you want to work flat, there are patterns for that too.