My advice is to only evolve your 5/4* girls. Get your 3* to around 30, which can be done with the crappy manyu, and then star evolving your 5 and 4 star girls. I'd recommend getting then to about 30-40 after evolving them as well. Ideally you should only use the matching manyu on each girl so you can maximize your xp gain. Also keep in mind every 2 weeks you get 1 free 5* from events and you should get a slow trickle of 4* from gacha seeds as well. If you get to the point where you've run outa 5/4 to evolve do a 3* of whichever type you have the least of so you can balance out your teams better.
Seriously, level your rarest girls and the ones you like the most. I started playing on DMM and i clear most maps easily despite only having one girl at evolved level 70. To my knowledge there is no gold girl that is worse than any silver. There is one silver that is a must to have if you can get her though - Lilac, because of her passive that lets you pass through webs.
(In fact I am currently playing with Mint 2* (Evolved and Maxed) to farm Tickets for her. I have also many 3* Girls Evolved (Level 60), with 4 Equipment slots they are not really weaker than a 4* with only 1 or 2 Equipment slots, they helped me a lot and don't regret the investment, especially if you lack of a specific Archetype (like me in the beginning with zero 4+* Pierce).
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What the 2/3*s lack in raw stats and skills they at least partially make up for in easily unlocked equip slots, lower costs to evolve (both coins and using lower tier dragons so fewer runs through the 80 stamina dragon maps) and more easily leveled skills. While they will eventually be replaced, they're not a bad investment per se early on.
Personally, if you're going to evolve 2/3*s, I highly recommend giving priority to the ones with high speed, since this is the one stat a 2* can beat a 6* in, and some maps have some wacky speed gap requirements to 3-medal them. After speed comes type (if you're lacking a specific one).
tfw your 2* waifu is slower than Lavender or Cosmos
Anchors are as useful, actually. To slow down that sanik teams with Alpina, Orchid Wylder and Edelveiss evolved XD
Probably a good but not the BEST idea, but sort your units in priority (High-Low) and level top-left to bottom right. I've noticed that units with higher rarities PROBABLY have better stats than those in lower rarities. Hit that normal gacha every day and see if you can get four-stars, and I'd say to throw out the three-stars that don't/wouldn't make it into the 3rd or even 4th squad.