You can do any or all of these depending on your other cultivation methods. If you have a giant open-air growing area in the desert, you can follow John Trager, If you have a set of t9iny pots inside your house maybe you would work differently. Different soils and different watering techniques also required different fertilisers.
My recommendation would be little (very little!) and often, and make sure you have trace elements if you grow in a pot. You are unlikely to starve a cactus of nutrients in any short period of time so don't panic about it until you have more experience. As with water, less is more, but none is not enough. I just made that up