Assuming you took my advice on the way to win 50. The next step is as follows.
Area - Do Not Set
Opponent Strength - Intermediate
Battle Record Status - New Opponent first
This should take you up to just short of 150. (I think I accidentally fought some people multiple times so it's hard to keep track). Then make up the rest of the fighters with advanced. Obviously if you're going for 1000GS you're going to need to fight them at some point anyway.
More of a note than a full guide. It has to be 150 unique warriors. You can't just defeat the same character 150 times. Therefore if you fight anyone multiple times you can't use your win/loss counter to track your progress anymore. hence why I recommend hitting the new opponent first. If you are unsure the people you have though show up in white text rather than green and say your previous battles to the right of the screen. (Well you can but just remember who you've fought multiple times)