We're considering a speed oven as a 2nd oven, probably 27". Our main range is an all gas 30" range. What are those microwave / traditional ovens combo good at? What are the best uses? Conversely, what should they not be used for? 
Yes, you can store an opened pack of dried yeast without a problem. Seal the pack as well as you can (plastic clips for just that purpose are very common, or you can just use an office 'bulldog' clip), and put it in the fridge. 