Any exposure longer than around 17 sec will show trails, so if you are working the Milky way, which it sound like you are, I would work with a ISO combination that allows you to get a nice noise ratio. Faster lenses, from Canon tend to show coma towards the corners, but this is very obvious (butterfly wings).
For focus, it's not really a huge deal, as you should be able to focus on a stationary object before dark (finding infinity) and then use that setting later on at night. This is what I have done for years now, Nikon, Canon, Fuji, Pentax, and P1. You can also go out and focus on the moon (I realize this is not going to help in your current situation), mark that spot on your lens for use later as if you can get the moon in focus the stars will be also.
Your blur on longer exposures, as already mentioned, will be trails.
Using Live View also works and Canon's is much better than most for night work. The trick is to figure out a magnification level in Live View that works as over mag, will make it hard to get the image sharp and under mag, is even more frustration. I would also try to pick a planet like Venus as it's always out low in the sky, and use that for your target, or a brighter star, making sure it's in the center of your frame.
Also check out Adam Woodworth's site as he has a lot of good tips.
http://www.adamwoodworth.com/Yes, you can pan for the Milky way, I would have the camera in the vertical orientation when doing this. Can't really do this with star trail work, at least I have never figured out a way.
Paul C