you need to take clones first, u cant or it would be a bad idea to flower a plant and then switch it back to vegg once its your mom, pick a couple plants clone them keep tabs on who is who, and then flower one clone each and u can determine your mom, also yeah dont over load you grow space 15 plants in 6x4 tray should be enough space but be weary on root growth, the rooots are ussually just as big as the plants themselves.