Painting with water based acrylic paint or with tung oil on the outside surfaces ONLY and doing it every 18 months to 2 years is all the care needed.
The bees will use any crystallized honey but it should not happen in the bee hive although it can happen after the honey is extracted.
The bees will not collect honey in the rain and there is no advantage in sheltering the hive from the rain. Rain reduces the nectar in most flowers.
That all depends on you maintaining the hive from the elements, in your area that is rain and moisture.
That all depends on the availability of suitable flowers, the weather, the strength of the hive and how far the bees have to fly to forage to give you just a few of the variables. Even two hives together will not give the same return of honey.