Thanks you very much John for helping make my ideas clearer about the trip:
Do you want to see the best scenery? YES!
Do you want to see what is uniquely American? Not a priority. I mean, non especially native American, but I'm eager to be in the USA and share for some time your beautiful country
Do you want to experience American people and culture? Yes, but i nthe sense that I would like to meet people all along my trip
Do you want to see the most famous places? Well, some
Do you want to meet other touring cyclists? YES. I wish I won't come alone, but I would appreciate to ride regularly with people met along my route.
Do you want a physically challenging route? NO!!! I like biking and I've often been on bike holidays but in Germany or France. It's not exactly the same as riding across the USA. Anyway I'll start cool, and I know that in a bout a week I'll grind more and more miles a day
Would you like a remote experience? I don't like car when I'm on my bike. I love being in te wilderness, but I don't like being noso to nose with a bear (anybody does?). Obviously the perfect track would be car-free, with extra views but regularly passing thru towns or services. I can manage some days of backcountry camping, but I don't want to be alone all the time.
Do you want other experiences, such as white-water rafting, climbing mountains, exploring cliff dwellings, hiking through the woods? Well, I would love to paddle on the Green or the Noth Payette... but I can't afford taking a kayak on my bike

As for hiking, yes, in the parks, to explore some spots that cannot be reached by bike, or just for fun.
Do you need to avoid the heat, or do you love the heat? I don't like heat, I wouldn't go in the Death valley in the summertime. but I'll take what will come.
Thank you all for your precious advice. I'll think about mixing up Sierra Cascades and Pacific Coast or to restrain the tour around Yellowstone, Wyoming/Montana/Idaho using the ACA network.
I've already been in the Candaian Rockies to hike, from Banff to Jasper, that's why I was rather interested in discovering the USA Rockies.
If you have more suggestions, that helps me a lot