My guess would be about 7-ish lbs as an adult, give or take. That's too bad on the yeast and the mites
, ugh. But it sounds like the vet is on top of it. The Otomax should take care of the yeast. What is the plan for the mites/mange?
As for the food, I feed raw (Primal), but for kibble the brands I like are Orijen, Solid Gold Barking at The Moon, Wellness CORE, Innova EVO...to name a few...