>>529401963
You need to mostly do tacet fields to gain the EXP items for leveling your echoes, but as a newbie you'll be swimming in materials from playing the story/permanent events and other map shenanigans, so no need to worry about that too much. Beyond that, you're free to farm the echoes themselves as much as you want to. There's also a nice bump at Union Level 40 where you can start using Modifiers to pick main stats on non-leveled echoes.