Start with continuous power
Add the power of the devices that genuinely run at the same time. This is the starting point for the continuous load on your system.
Allow for start-up peaks
Motors, pumps, compressors and some chargers can need a higher output briefly at start-up. Check the equipment specifications instead of sizing only for average use.
Leave a practical margin
Plan for additional equipment and changing work. For critical applications, a short technical review is sensible before choosing a final configuration.