We're going to Canada!

I am now in charge of changing our upcoming Seattle trip to a Vancouver Canada trip.  I have been searching for a VW bus for YEARS now and I finally found a great one.  The best part about finding this one now is we actually have the money saved up to buy it.  In the pass when I would look, I never had the money in the bank.  I would find a good deal on a  bus and then start looking around the house thinking, "what can I sell really quick!"

The guy selling the VW lives and works in Vancouver but happened to be in Seattle over this ast weekend.  This was great for us because my brother-in-law very happily met with the seller and inspected it with a fine tooth comb.  He even checked for rust under the floor mats!

We are ready have tickets to go to Seattle but now I need to make a few changes to the trip plans.  *Side note: we love Seattle because their are WAY more granola muchers up there.  Plus they have the best gluteen free pizza you've ever had!*

I'm not always good with the details so feel free to help me out if I've forgotten anything here.

1. I need to change our tickets from round trip to one-way.  I want to find the cheapest (least amount of fees) way to do this.  I also want to make sure I get credit towards a future flight with Alaskaair
2. Because we are going to dry the bus home, we are thinking of mailing our sleeping bags and cold weather gear to Firefly's brother.  I don't want to pay $15 per checked bag nor do i want to carry a sleeping bag onto the plane with us.
3. I need a way to get from the Seattle airport to South Lake Union mid Friday morning while the brother is at work and then for three people to get back to the airport about 730 the next morning. (My brother-in-law is carless and we can't all fit on his bike...I can rent a car for the day/night if i need to but would rather not)  Any ideas? how about car sharing rentals in Seattle?
4. From the airport I'm thinking we'll take the train up (4 hours...back to bed!) $26 each is all.
5. Now were in Vancouver with a bus and need a place to camp?  I think the beach sounds like a great idea...anyone know of any camping friendly beaches in Vancouver?