First klipper install on an old printer - should I flash the board back if it goes wrong?

The pin name mismatch is completely normal, you're looking at the right config. Klipper doesn't use the labels silkscreened on the board, it uses the actual pin names on the processor itself. So where the board says X- or E1 or HEATER0, the config will say somethig like PB6 or PD3 depending on the board revision. The community configs for the common Creality boards have already mapped all of that out for you, so trust the sample config over the silkscreen. The only thing to double check is which board revision you actually have, since some of them shipped with a couple of different versions and the stepper sockets can be wired differently. There are threads out there on how to tell them apart visually, usually down to the chip markings or which CPU is on it.

Seconding the board revision thing, that bit me on my second printer. I had the config for one variant and mine had a diffrent stepper layout, took me a weekend of one motor running backwards to figure it out. On the flashing worry, don't stress it. I've gone back and forth between Marlin and klipper on the same board more than once, you can always reflash the old firmware again if you want to revert. Worst case is a bad flash and you redo it with the pi off the board, nothing permanent.

The scattered docs thing never really got fixed, it's just how it's always been. Back when I started with 8 bit boards we were editing Config files in notepad and hunting through github issues at midnight, so honestly klipper is a step up. My advice is start a notes file the first week and write down every fix you find, because you'll hit the same problems again on printer number two. Also grab a spare SD card and image the pi before you change anything big. A fresh image takes ten minutes to rebuild, a borked one takes a whole evening.

Following this because I'm in the same boat, only mine is still stuck at the part where the little computer talks to the printer. Mine connects fine but the screen on the printer went dead once the new firmware went on, and now I'm not sure if I broke something or if that's just how it works now. Does the screen stay useless the whole time or can you get it back later? Right now I'm doing everything from my laptop web page which feels weird but I kind of like it already.

For me the thing that finally made the pin mapping click was just opening the sample config and my old marlin config side by side in an editor with a split view. Sounds dumb but seeing fan pin next to fan pin, heater next to heater, made the whole renaming thing obvious in about ten minutes. Before that I was jumping between browser tabs going cross eyed. Also did a continuity check on the heater and thermistor pins with a cheap multimeter before first power up, just to be sure my board revision matched what the config assumed. Took two minutes and saved me from cooking a heater cartridge on day one.