I sow 3-5 seeds in a cup. The seedlings get really crowded before I can get them transplanted outside. When I remove them from the cup, the roots are all tangled together, but with a hose spraying water on the roots, I can typically untangle them without breaking any roots pieces. The growth in the cup slows down when they get that crowded, but I've had to keep them in the cup longer than anticipated and they did fine. Sometimes the smallest plant will die, but usually they all do okay.
I just sowed another 50+ seeds in cups. I have NO idea where I am going to plant them when they need to be transplanted outside.
What lies behind us and what lies before us are tiny matters, compared to what lies within us. Garden Rooms and Becky's Budget Garden