well, you can go and get yourself professionally fitted (about $150) or use wrenchscience.com to determine sizing.
As for testing the stems, you should be able to go to your LBS and try a few different stems for test rides to see how different lengths and rises feel.(If you do that, Please don't then go buy a stem off the internet just because you can get it $5 cheaper).
As for cranks, most use 175mm, and most bikes come standard with that length, except for very small bikes may come with 170mm. Again, your LBS may have cranks you can test, but I wouldn't be surprised if they only had 170mm and 175mm (maybe 172.5 and 180 if you're lucky)