I would get medium ones. They usually have alot of small ones in there also. They are soft bodied so if they are a lil big they are ok. how many depends on the beardie, give him as many as he wants to eat in 10-15 mins. I just dropped them in a little dish and put them in my beardies cage.... she goes nuts for them runs right over and gobbles them up. She is closer to 6 months old but was eating 20-30 worms twice a day. If you buy crickets in bulk you save a TON. I dont know if pheonix worms will be cheaper.... but again you would save alot if you buy in bulk. Ideally they need to be kept in a cool place around 55f, but dont stick them in the fridge... thats too cold. A wine cooler, in your garage, or in a cool basement would be best.