1) There is a mission editor. I have never used it, but I know it's there. In the below linked thread there is a recommended mod, GWX. It comes preloaded with a whole bunch of new single missions and a way more historically accurate campaign.
2) That's why you don't use them. They are bugs left over from the devs, and were never fixed. You have to manually move the crew yourself. Double clicking the compartment name will minimally staff it. Right clicking it, then double clicking individual crew members will move that crew into the compartment.
3) I dont know, I dont use the grammy, I use Pandora in my browser. But i run in a windowed mode so I can mute it to listen to the hydro when I want.
Steam is fine (got mine last fall when it was on sale for $3, so :P ). That's what I run. There are a couple draw backs. Check another thread that was started today on issues to have to do with the steam version.
http://www.subsim.com/radioroom/showthread.php?t=181694