Weld schedules are available the Resistance Welding Manual and AWS Standard C1.1 for many of the most frequently used materials. The information commonly provided is the proper electrode design, size and material. The weld force, weld time and weld current are also published. The minimum distance between welds if usually listed and the expected nugget or button size is shown. Tensile properties frequently are also published.
All of this is good information to use as a starting point. Each application will dictate some variation from these settings. These numbers will act as a good guide or goal for your application.
I suggest a purchase of a copy of AWS Standard C1.1. It has a complete set of data that you can use for initial set up. Then fine tune for your machine, product being welded and desired results.
References: AWS C1.1 Recommended Practices for Resistance Welding
RWMA – RWMA Resistance Welding Manual 4th Edition