Hi Robert,
The batch size in netEvaluate is actually 1, so there is no way to decrease it and in case you want to get the batch of outputs you would have to map netEvaluate on a list of prompts. Do you get those errors from a fresh kernel?

Try to use the ResourceFunction["StableDiffusionSynthesize"], it has similar options. Here are some examples:

1. Generating a single image: ResourceFunction["StableDiffusionSynthesize"]["A cat in party hat"]
2. Generating five images based on a single prompt: ResourceFunction["StableDiffusionSynthesize"]["A cat in party hat", 5]