Originally Posted by
Oz1337
I recommend you go for 300K for each item first, you can cover nearly all costumes and extra stuff that only unlocks if you have X amount of doujin items. Once you've done this, just focus on reaching 500K for all of them to unlock the last ones. Once all extra stuff is unlocked, you can focus on one of the items until you get 1M for each.
Basically this is the priority if you want to unlock all the new stuff first in case you can't complete the event. If you're not interested, simply focus on your favorite doujin item depending on the items you get in exchange.