"When I enter zone, pH and soil (loam, silt) and try to get a list I'm given a message that there are too many plants to search. What am I doing wrong?"

Some soils and zones can grow most any plant especially loam with neutral pH.
Add a function or do each plant type separately. Trees, shrubs... This is best.
They can be tabs in the excel file if you drag them in/on to one file.
Either way be more specific on plant characteristics.
Do a food list or N fixers...