Pots and soil limit growth for large plants such as tomatoes, kale and broccoli unless you go with barrels. However you CAN use Kratky to grow such plants in a single 3.5 gallon bucket. Kratky is a passive, simple hydroponic method that does not use soil. I regularly combine multiple plants in a single Kratky 3.5gallon bucket. When combining plants in a Kratky bucket, you would need to consider how the foliage interact since nutrition is less important because of availability. For example, snow peas and tomatoes can go in the same bucket.
With pots and soil, your options will be more limited. My potted plants never do as well as their clones in raised bed or hyrdoponics. I only combine herbs in pots.