Get 25 Pikmin. At least 23 should be flowers. I chose that as the minimum number of flowers because it seemed to me like a good trade off between getting a powerful army, and waiting too long for planted Pikmin to mature. Getting 25 flowers is ideal, but be sure to have a good book for the long delays while the Pikmin mature.
If you need more help on this level, you won't find it here.
On to day 2.