Hello my fellow Roadtrippers!

First of all it's great to be back after a few months away. I couldn't do my US roadtrip for multiple reasons but this year things seem to be going in the right direction. I just need one more confirmation from my wife's job, and if so, we're on the way.
However, I am posting this thread seeking your help with the route, choosing roads, saving time, sightseeing... I have many ideas, and I would like to share them with all of you and benefit from your knowledge. Plus, I have many doubts.
But first things first, some info:

Flight:
Being portuguese we are flying from Lisbon (or Madrid) to Seattle in the beggining of September (perhaps on the 1st) . We fly back to Portugal on the 20th Sept. If the ticket fare allows to be split in half, we'll make LIS-SEA and then SDIEGOorLAorLV to LIS. If it turns out to be too expensive, we'll just make LIS-SEA-LIS adding a domestic flight to take us to Seattle from one of those 3 cities.

Lodging:
Being on the road and "respecting" the Roadtrip philosophy, I won't be making many prior hotel reservations. Perhaps, only Seattle. On the road, I have in mind the International Hostels, Motel6 and whatever comes our way.

NOW, the real thing... the Possible Itinerary
(still just lots of data, nothing concrete yet)

WASHINGTON
Seattle (2 days)
road from Long Beach to South Bend/Raymond
Long Beach Peninsula
Cape Disappointment
Ilwaco

OREGON
Astoria
Seaside and Cannon Beach
Tillamook
Portland
Mt Hood and Oregon Cascades
Depoe Bay
Devil's Punchbowl
Newport
Florence (Sea Lion Caves and the Dunes)
Bandon
Gold Beach
Brookings

CALIFORNIA
Crescent City
Redwood National Park
Eureka
NAPA region
Muir Woods
San Francisco (3 days)
Santa Cruz
Monterey
Carmel
Big Sur
Pfeiffer State Park
San Luis Obispo
Santa Barbara
LA (3 days)
La Jolla
San Diego

This is of course a rough idea. Now.. comes some questions. I can't wait to read your views on this matter. Here it goes, no particular order:

- 3rd of September, labour day. Can I find a car rental agency open this day? Is anything open?
- Car insurance? How does it work? Can it be done in the rent-a-car agency?
- The car itself. I am thinking of an intermediatte. My internet searches tell something like a $1000... :S (Ex: Pontiac G6) We're just to people, but beinga a car enthusiast, I would like a nice car to drive, roomy, reliable.. What do you think?
- In what items can I have good discounts by paying with American Express? I can't find the american express discount partners anywhere.
- What to do, what to see in Seattle?
- Should I go to Portland? If so, what are the highlights of the city?
- After Eureka, should I keep following 101 to San Francisco or should I catch the 299 to Redding and then the 5 to save time? Or even doing Portland-SF by 5?
- National Parks... most people say that one must go to Yosemite. Should I? What to expect in terms of doing? And time? 1 day? 2 days?
- Just out of curiosity, what is the Tioga Pass and why do they close it seasonally?
- After all this trip from Seattle to LA... without any prejudice to any city.. should I choose between SDiego or LVegas?
-From SF to Santa Cruz. Should I take Highway 1 or a faster one? How's the scenary?
-"Tokeland/Grayland/Westport" Are they worth the visit? Or should I just stick to 101?
- I was told that the trip between LA and SDiego by highway 1 has some beautiful sights but also other ones that really don't matter so much. What's the better way then?
-Being portuguese, can and/or should I become a member of AAA?

That's all the questions I can remember by now... :)
Mind you that I am aware that 18 days are not enough to see all these places, but I am counting you all to help to select some of them and to optimize my itenerary in terms of time.

Thank you very much for helping! Start your answers! :)
Ricardo