Thank you all so very much for all your help (and also for the compliments about my english!). You are all being very kind!
I'll definitely post a more "decided" route in the coming days or weeks, and hopefully you can give me some more suggestions about "hidden gems" along that route.
At the moment, I'm trying to persuade my old folks to join us on the trip for a week or two, so hopefully I'll have some luck with that!
One last question: is it difficult to find accommodation with short notice close to the national parks (and maybe also close to/in the big cities)? Otherwise, it would be hard to be spontaneous on the trip if you have to book these motels a long time in advance.
Take care, all of you, and once again thanks for your time!
/Daniel