If you blow it up enough you will see more of an issue than a scratch. If it was just a row of stuck pixels you would not see areas above and below affected.
Probably won't see much on the forums about a 10 year old cameras... For pentax K20specific information try https://www.pentaxforums.com/camerareviews/pentax-k20d.html
I have done both the Durango and also the Cumbres and Toltec. I prefer the Cumbres and Toltec. I liked the Deluxe Tourist Car ( second from the back ) as the car in front was Open-Air Gondolar ( NO Windows ). I spent most of my time in the Open-Air Gondola car... It is like standing up in a Convertible watching the world go by. Would suggest watching the many online videos before making your decision.
This issue with long HDMI cables is that they are thick and heavy. I have had the HDMI Connectors break with just the weight of the cable hanging on the end of the cable.
Anything over 15ft I use HDMI over Ethernet Cable .
HDMI Cable ???? Are you sure you are not talking about a USB Cable ??? HDMI is video - not suitable. 5 meters is the normal limit for a USB Cable. You can go longer in some cases than 5 meters. ( I have )
Better to get a few smaller cards than one big one... If your one big card fails all is lost... If the pictures are split between 3 or 4 cards you only lose a small portion of your trip. Cards are small so space is not an issue.
I buy from Amazon all the time - they do offer memberships but you do have to "Agree" first. I have never seen it added without you agreeing to it first. Lately it has been a 1 week membership for $1.99 great if yoiu want fast shipping for that week - but you do have to remember to cancel before the week is up.