Welcome aboard, Chris!
If you're scared driving your car on the street, you'll definitely want to do something for Targa! In 2008, we hit a speed bump at 80 mph that wasn't even in the notes because, well, it wasn't exceptional. Lift the car, add a skid plate and make sure you're comfortable over just about any paved surface. I seem to recall a Subaru driver telling me they ran gravel suspension screwed down all the way.
In 2008, we had two people for crew: my parents. They weren't a lot of help in wrenching, but they took care of the background details like checking us in/out of hotels, getting dinner in the evenings, checking tire pressures, filling camelbaks and cleaning windows. All the stuff that needs to be done but eats up time. They also met us at various points when we needed help, such as a roadside setup with jackstands so I could adjust suspension height between stages. That worked pretty well, but if we'd had mechanical problems I would not have have had much sleep.
In 2011, we had a cast of thousands. Or at least, it seemed like it. Two cars, five crew. We had one rock star member that was more mechanical and able to take care of the cars well, although the two drivers were still the crew chief for their respective vehicles because of greater familiarity with the cars. The rest of the crew played a similar role to 2008, although there was now a food truck in the parking lot of the evening services that served some very good food. That made evening meals much easier.
Some teams don't even have crew, especially in Touring. The teams work together - we carried some spares for an Alfa in 2008 and a number of other teams helped us out in 2011 with tools we hadn't thought to bring. A number of teams will advertise in advance if they have room or are able to support your car.
We trailered everything there, then dropped the trailer in St. John's. Everything we needed was in the back of the pickup. I didn't have a massive collection of spares, but you need a spare tire for a Targa class car (assuming you carry another on board) as well as various consumables. I also had replacement suspension parts just in case there was a whoopsie as well as other potential failure points such as a coil. Which I used. If you're driving a fairly common car such as a Neon, you will be able to source some parts on the island. Heck, they found an engine for an Exige last year, and in 2010 Kia tore apart a brand new car to yank the drivetrain to replace a blown one.
The route is public knowledge and there's nothing stopping you from doing recce. However, it's a long, long race and that's a pretty major undertaking. Personally, I didn't do any with the exception of one stage where we'd arrived early and had time to kill. I also watched some videos, this was particularly useful for Greenspond. The official route books were released about a month early this year which was nice, although we didn't do much with them.
Here's something I put together in 2008: a marked-up route book and a narrated video of one of the stages. The tightest stage, don't let it freak you out too much 
The books are evolving a little bit, they now have better verbiage for the navigator and apparently they're also going to be adding more turn-by-turn detail. At the moment, they only include navigation and turns that are "out of character". On Brigus, of course, it's all navigation.
My wife Janel gives better instructions than just about any other in-car I've watched, you'd never know she's a novice here. This is what your navigator should aim for: accurate, concise and well-timed.
Route book (PDF)
In-car video with subtitles
To get an idea of what's typically in the route books on a faster stage, listen to the notes in Garnish. This will apparently get more detailed in the future. You can hear how Janel changes inflection in her voice to differentiate between the different types of information.Garnish
