For the out-of-country passenger who has never used UK rail, would it not just be easier/less stressful to buy the tix online, pick them up at a kiosk at the station, and then avoid any glitches or issues? Or is it even easier to just tap a contactless credit card when entering the train queue?

Having never done this, does each train track have a separate entry machine, so they know exactly where you're going and what to charge you for that specific trip?

(We won't have Oyster cards as this will be our only train/rail on our trip).