I currently own 13 Raspberry Pi computers, I started with the first model 1 in 2012. I use a couple to monitor and log various temperature sensors inside and outside my house. I have created a Raspberry Pi Community where I post about a robot I am building with a Raspberry Pi. I have been sidetracked lately trying to run digital mode communication with one of my rpi's connected to my Ham Radio. I have created a Ham Radio Community for my Ham Radio projects.
I use the default Raspberry Pi OS (debian based linux) in all of my rpi's. I have been a Linux user for 20 years.
The Raspberry Pi 400 is a Model 4 with 4GB Ram all built into a keyboard. If you get the kit all you need to add would be a HDMI monitor or TV for a display.