It’s counter intuitive but less plants with a larger canopy space will produce better fruiting.
The roots are strong and can support a significant canopy, but also to grow as well as they can they are greedy and need that canopy.
As for coplanted tomato and peppers they have similar water requirements when together, water for the tomato and the peppers will do fine. Just not the other way around.
You of course know what works best for you in your specific setup