klipper is the firmware flashed to the printer
gui is achieved and accessed through mainsail or octoprint. I haven't tried octoprint.
mainsail runs on a raspberry pi and can manage multiple klipper printers with one device. you can also add klipperscreen, it's an addon that can be used with a touchscreen for an interface at the printer (or anywhere really)...
but I just access mine running mainsail through my phone browser or the laptop I use to model and slice. I like orcaslicer because it integrates mainsail right into a tab in the slicer and provides a seamless user experience.
typically the fan cooling the heatbreak and extruder stays on even with the "extruder" aka part cooler fan turned off