2nd artifact -> scarab rare
10th artifact -> ring
130th artifact -> pet (cooles fucking pet ever btw. go swimming with that pet and be amazed)
170th artifact -> qiraj mount
thats roughly the numbers it took me. I'm currently at like 230 artifacts and still waiting for the wand and the sword. as it has already been pointed you should use the pandaria digsites to get the achievements while farming the mount/pet.