As everyone have been saying, farm some manyus and prioritize leveling your 5* and your 4*s. Eventually, as you gain new girls, you'll swap out your 2* and 3*, so leveling them could be a waste of materials. You can try faming manyus with stage gardens, it's a nice way to gain exp too. Farming for gifts is valuable as well, as long as you keep prioritizing 5* and 4*.
Once again as people already said, evolving 2* seems like a waste, while 3* can be useful. However, I don't evolve anything bellow 4* since my goal is to swap out my remaining 3* as well, so evolving them seems like a waste of gold imho. But whoever you decide to evolve, just don't farm the dragon missions unless you're really about to evolve a girl, and get the girls to level cap before farming lvl 100 dragons if you need them.