Totally agree about the keyboard and processor/ram. Originally thought about getting the X13, but I recall the screens options weren't that good, and I prefer the larger size and bigger battery anyways.
As for Linux, I fully intended to dual boot Arch and Windows. Due to circumstance, I am stuck with a tiny 128GB NVMe and so I am using the default Windows for now. I've been watching this playlist of a user installing Arch on their T14s to help prep me on some of the quirks: https://www.youtube.com/watch?v=ihFPynCqfzc&list=PLiKgVPlhUN.... I hope that helps answer some of your questions.