I've been to each several times. Quito is 2800 m elevation, while Cuzco is 3500 m. I'm mid-50's and overweight, and on my visits to Quito the altitude I find far less noticeable than Cuzco. In Quito, I just huff and puff going up hill. In Cuzco, I feel lightheaded and can feel out of breath even sitting for the first day, not to mention waking in the night in a panic gasping for air. I think you'll be OK in Quito.

Coca tea is great... I drank it like water in La Paz (pushing 4000 m), but provided no relief whatsoever.