Sorry for the beginning I forgot the edit the downtime out because I was rushing for work T.T. I found a really nice early stage for grinding. The Battle of Hitokotozaka in Chapter 3. This battle spawns enemies almost endlessly and has straightforward objectives which makes it a great first place to start grinding up resources, money and levels.
Simply play through the mission like normal while completing objectives as best as you can. Nothing tricky, just a great stage for grinding!
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