There's a nice rule for preventing star streaks. Lets say your using your 50mm lens, 450/50 = 9. This means you can have a 9 second exposure before star trails can be seen. So the rule is divide 450 by the focal length you are using. (e.g 18mm = 25 seconds)
As for ISO you'll have to use a fairly high ISO (800-1600)
If you're doing deep sky photography I recommend you take multiple pictures so you can stack them using software like (
http://deepskystacker.free.fr/english/index.html)
To reduce noise from the sensor take a dark frame after shooting, (just take a photo with the lens cap on using the
SAME settings you used to take your other photos). You can then use this dark frame to subtract the noise from your images.
I think that covers the most important things.