One good thing about ThinkPads is that most of them do not have their RAM soldered to their motherboards, so it is easy to buy your own RAM on NewEgg and then augment or replace the machine's original memory.
in general, thinkpads have good support for linux. i've had various x series laptops over the years and they've been very solid (more so than my partner's macs, where i need to keep replacing fans and power cables).
for desktops, just build what you want. as long as you avoid strange or very new hardware it generally just works.
But as far as I know, unless you go with some obscure distro, most things work.
There are often quirks about laptops going to sleep or hibernating, and sometimes integrated sound cards, but it's really hard to predict in advance, I found. You could look up each hardware pieces by brand and see how well they're supported on linux. Often you should find results in google by using the model number, the brand and 'linux'.
To sum up, based on my experience with debian's, slackware and openbsd, it will depend on the distro and the exoticism of your hardware.
HTH
Also if I price it out, it equals a T530 or W lenovo with specs. I would buy ssd and ram externally from newegg
I had an HP dv7 series machine before this and that was a great Ubuntu machine as well, although it required a little more tinkering. This series of laptops have major overheating issues though with temperatures going north of 100 degrees Celsius if you put it on a flat surface without a cooling pad.