Welcome to AFF.
Wow, that's quite a list of questions you pose, and interesting, too. Thewinchester has already started on the matter of points and airlines, and I'm sure that others, far more knowledgeable than me on those matters, will join in. So let me just address the matter of your surface itineraries in North America. I have lived in the regions where you propose to travel, and know them well.
First to your question, "Are we mad?" to try to do it all in four weeks. The short answer is "NO, you will have a fabulous trip," but the longer answer is "YES, you need to make some adjustments to what you are proposing."
Everyone's opinions on what is worth seeing will vary, but remember that both USA and Canada are very rich in places of interest so that inevitably you will be forced to make choices.
Four weeks equals 28 days. Cut out a couple for travel and recovery each way, so let's say you have 24 for touring. As a first pass I would suggest splitting that into 19 nights on the East coast and 5 around Vancouver. (But I'll make a 14/10 split further down).
Regarding the East coast, I consider the northern half to be far, far more interesting than the south. In fact, I readily rate Florida among the ten most boring states in USA. So my first suggested amendment is to fly from LAX to IAD (Washington) and forget about FL, GA and SC. There is another reason. Rental cars are relatively cheap in USA, but drop-off fees to remote places can be steep. If you flew into IAD, you could make a fabulous round-trip in the North-East, including Canada, come back to IAD and fly out of there to Vancouver.
Consider something like this as a route: Washington, Philadelphia, New York City, Connecticut coast, Rhode Island, Cape Cod incl Nantucket, Boston, Quebec City, Montreal, Ottawa, Toronto, Niagara Falls, Gettysburg, Shenandoah National Park, Charlottesville and back to IAD.
Now on the west coast, after seeing Vancouver itself, rent a car and tour to Whistler, Victoria, Seattle and back to YVR to fly out. This will require car ferries onto and off Vancouver Island, going over with BC Ferries from Horseshoe Bay to Nanaimo, and leaving the island with Coho Ferries from Victoria to Port Angeles.
Can I suggest that you buy yourself a Rand McNally Road Atlas for your planning - invaluable - and you can probably pick one up at a decent bookstore in Perth. If not, get someone going to USA to buy you one - dirt cheap over there.
If your wish to start at Florida was motivated solely by a desire to take the kids to Disney World, I would satisfy that desire simply by spending a day at Disney Land (essentially the same thing) at Los Angeles en route.
Now what about the 14 night/10 night split I suggested? You could make the east coast circuit tighter, but in the west you could add in a circuit from Vancouver out to the Canadian Rockies (Lake Louise, Banff), as well as what I suggested above.
Plenty to think about there, and others will have ideas too. Feel free to ask questions.
