As of now, I have 4,652 crystals and i don't know what to get. I have shaft, thunder, isida, smoky, hunter, hornet, and viking, What should I buy or upgrade. Please help!

So i have recently leveled up to Sergeant-Major. YAY! Anyways, I have 3,692 crystals which I do not know what to do with. I now have an isida, thunder, shaft, smoky, viking, hornet and hunter. They are all M0. I use a thunder and a viking mostly. Can you tell me what to buy or upgrade? I think I'm going to get m1 and m2 and so on for the thunder and viking. What do you beauties think?