For practical GEO systems avoiding obstructions, what number of satellites is often proposed beyond the absolute minimum?

Four or five satellites

While the absolute mathematical minimum to achieve complete, continuous Earth coverage using geostationary satellites hovers around three units spaced evenly along the equator, practical implementation often requires a slight increase in hardware to manage real-world operational challenges. For practical purposes, engineering systems frequently propose utilizing four or five satellites positioned in the GEO ring. This slight surplus accounts for necessary considerations such as ensuring robust coverage overlaps to avoid terrestrial gaps, managing potential signal obstructions from terrain, or guaranteeing that a communication connection is never lost during the necessary handoff process between adjacent satellites, thus moving slightly beyond the theoretical baseline.