You have two bikes. In unlikely scenario when something go wrong, you can use one and take another to mechanic later.
Done that, one is in for repair now under guarantee
It is easy when you have right tools. What you need is a quick link with you all the time. Anticipate what can go wrong on a trip like that and take stuff with you to quick fix common faults. Spare inner tube, quick link, pump etc.
As for punctures that is one thing I am 100% OK on
No, you don't always change chain and cassette together.
What cable are you talking about? I have never changed any cables during routine maintenance.
Gear cable, I was told better to replace as they are cheap
Watch few. It helps.
Or better check if there is a bike charity nearby. They organize courses and teach bike maintenance.
You can buy rubbish cheap bike and train on it.
Not a bad idea