A couple of things:
1) You typically do not want to cold crash the beer as opposed to gradually bringing it down to lager temps. You don't want to shock the yeast. That being said, it's not the end of the world. Note for next time.
2) How long to lager? Well, how much yeast did you pitch? Did you make a starter? If you had a sufficient pitch, you could consume in 3-4 weeks. If not, I would leave on for 4-6 weeks to let the yeast finish their job cleaning the beer. What temp did you ferment and for how long?
3) You can prime with sugar for carbonation or force carb when it is done. Up to you.
Hope this helps and good luck!
If you have done a D-rest and cleaned up all of the VDKs and such, you can crash it down so that the Stokes law thing is going for you.
Look at Kai's site (Braukaiser.com) and see the different profiles of temp and time.
This is why I asked my second question. If there was not a sufficient pitch, then a 3 day D-Rest may not clean up everything and gradual cooling may be preferred. Kai is assuming a proper pitch rate. I still think gradual cooling is best practice, but that's just my humble opinion. As stated, you can make great beer by crash cooling as well.