1. We went to Alaska in 2008. We left on June 23rd, right after our grandson's birthday. We did not go on a caravan for several reason, primarily because we do not like being tied down into a firm schedule. we talked to several people who were on caravans and most seemed to enjoy the company of the other members of the caravan. I looked up several caravan iteneraries prior to leaving and took note of some on the stops. I suggest you go to the Motorhome Forum and check out the Alaska forum for people who have taken caravans.
To answer more of your questions:
2. We did take a toad. We used it a lot in Calgary (we timed our visit there to go to the Stampede, which is a MUST SEE. We used it in Alaska quite a bit since we stayed multiple nights in various places. I would not go without a toad. It also came in very handy when our engine blew in the middle of nowhere.
3. We will go back in 2013 and will plan to leave Florida in late May and return after Labor Day. Summer is the time to be there, and that is when the Salmon run.
4. Other than the blown engine, which was caused by a factory defect, the only "wear and tear" issues were a Aqua-hot problem caused by the replacement of the diesel, one a/c compressor that died on the way home, two small windshield chips, and some loose screws.
5. We had no tire issues whatsoever and did not carry a spare.
6. There were very few miles of gravel road. Most gravel sections were areas under construction.A portion of the Cassiar Highway going to Hyder was gravel, but was well maintained. It really isn't a problem, just go slow. A bigger problem are frost heaves. Some of the raods were worse than others, but when you see orange cones or flags on the side of the road, you really want to slow down.
7. Repair services are pretty much limited to the larger cities. Anchorage and Fairbanks have several RV repair facilities, but outside of those, you need to be able to fix small problems.
8. I thought the ferry would be a viable option, but it is very expensive and the schedules did not fit ours very well.
You didn't ask, but Alaska isn't really any different from the lower 48 as far as services and supplies. There are Walmarts, Home Depots, and Fred Meyer stores ( which are like Walmart, Home Depot, Sears and Publix, all in one store). You can pretty much get anything there that you can get down here.
Have a great trip.