If you do paint, I recommend that you use semi-gloss or high-gloss paint. Mold and mildew have a much harder time growing on the glossy surfaces. The gloss is created by using smaller sized paint pigments and, thereby, a finer surface finish with less holes is created.
What destroys wood is moisture, plant growth (mildew, etc.), and bugs (termites, etc.). Keep the wood away from these and it will last a long time.
Unless you are putting wood into contact with the ground, preservative is usually never used. If you are using a wooden hive stand you might consider using creasote on the stand only. This has to be soaked into the wood. It's used on fence posts, railroad ties, etc., and it will protect against the problems of wood coming into contact with the earth.