I bet the shake at speed is from your tires. I had Michelin X series on my car when I bought it and replaced the fronts with new Bridgstone touring tires last fall. Tire shop guy said that people swore they were as good as M's for 1/2 the money. They SUCK! Have had to have them balanced 4 times in 5 months, over 1/2 the tread gone in 20k miles (70k tire) and they vibrate over 80 no matter what. I am going back to Michelins as soon as I can and plan on getting some money back for the garbage tires I have on the front now. Last balance job the Michelins were fine and have less than 2 ounces of weight on them, rt. front Bridgestone has 7.5oz of lead, left front has 9oz. They also have what I call belt separation in the sidewalls, tire shop calls that "normal" and "all radial tires get them". Can't explain to me why the Michelins don't have this problem.
As far as replacement of the oil pan it looks like a very easy job. Nothing in the way, just drive the car up on some ramps (I hate jacks when I am under a car) and take it off.
It sounds like you made out pretty good. At least the shaft you hit didn't take out a steering component while you were buzzing down the highway. That could have been the end of the car.