The Problem i have with Nation Battles is that you have to use 3* to make a Setup with 20 Girls from each Country. I like to hoard Manyus and Ampys before i use them (because Gold Efficiency) and 3* Girls fill your Character Capacity way to much. So you have to spend FG to increase your Character Capacity and i prefer the Gems to participate in a 10+1 Gacha Roll. My Character Capacity is 150 atm and i think i have to increase it to 200^^
What are the Rewards for Nation Battles btw? I don't know much about Nation Battles right now. I mainly plan which Girls i want for the future and have studied the 5* and 6* from the Japanese Wiki...