I would plan for softies much the same way you'd plan for sps.
They will contribute to your overall bioload, as they respire at night just as fish would. They wouldn't nearly require as much "calcium /alkalinity" load, so you could probably get away without a CA reactor on the tank, but a kalkwasser drip would still be recommended.
I'm interpreting your use of "bioload" as it figures into the demand of an efficient skimmer. You will most assuredly need a good skimmer if you're intending on keeping soft corals. They produce a lot of slime and emit a lot of toxins.
They also can take up more space quicker than sps can. So, plan accordingly.