I have a 70s kitchen with a very long countertop. I understand that I only need one GFCI to protect the downstream outlets (for example near the sink). However, I decided instead to install 3 separate GFCIs, by using pigtails going into the line connectors on each unit. While it may seem redundant, my goal is to make it convenient and clear for anyone in the house to understand which outlet tripped. My question is whether this is an okay setup. 20a circuit for 3 of the. 12-2 wire.
Yes, it is OK, assuming your work to pigtail everything is done correctly (hot, neutral, and ground all pigtailed, with the box also grounded if it is metal). You can test each receptacle individually with others in on and off states to be sure.
I assume your location is North America based on the circuit capacity and nomenclature used for wire sizing.