Hi! You should focus on them one at a time. I believe saving around 200 to 250 medium refines to get yourself to lvl 7 refine and around 150 adv refine to get yourself to lvl 8. Most players keep their refines similar at lower rank, but it gets less beneficial as you get higher in refinement to keep them similar. I recommend to always make use of refinement rebate for wish credits and upgrade equips one at a time to lvl 8 refinement.

~Jib