Hello @deborah,
I have moved your topic to bread processing for better exposure.
Generally for a poolish preferment you can use between 80%-100% water, in ratio to the flour weight. For 25KG that would be 20-25KG water. Yeast amount depends on what you want to accomplish in fermentation time and flavour. This can be very little, or up to all of the yeast to be used for the final dough.
If this does no answer your question, please do provide some more detail that we may help you.