I suggest you make a list of AW fodders you need like http://harem-battle.club/millennium-...-template.html
I myself used Vlookup for a slightly easier version, but you're still gonna need to spend some effort to make a list for your own.

after making a list (only include those maxed level, and thus ready for AW), feel free to CR/SU golds as well as to cc silvers to use as AW fodders. especially if you have excess.

If you're afraid of lacking fodders, select a couple more that are extremely high priority which you should level to max ASAP (such as nanaly)

as for rainbow...as tenhou said, maribel/sophie. frankly speaking, Sophie SHOULD have higher priority IF you're willing to wait for maribel and odette's revival events to come. even more so if you have equal or better alternatives. (although it's only recently added in DMM, but DMM revival units now have x2 SU chance fairies and x2 CR chance revival units, so you can eventually get a perfect version of them there)

regarding the current event, only farm the maps where you need specific silvers. I don't think anything else is worth it (in particular only valk drop in 1st map and pirate drop in 3rd map. 4th and 5th map are pretty blurry, not amazing enough to farm but not all too horrible either, since double silvers). even if you decide to farm, remember to farm monday daily for plat armors. you're in quite severe need of them (as well as fairies for using with exp armor)