I understand you perfectly. I also dream of a range of up to 600mm, but I think it will end with dreams haha. Maybe someday. 200mm of better quality glass should give a better effect than 300mm of weaker. With this range, you still need a croop. Camera on a tripod, manual focus (this is the basis!). With the moon, you don't have to raise the ISO too much, and don't open the aperture on this f2.8 completely. The exposure time is also not too long because the moon is moving. It's about to be full, so it's time to act :D And I recommend generally not photographing it at night. Preferably during the blue hour.