One of my favourite single missions in GWX is Evacuation! It is a lot of fun because basically it puts you in the middle of a lightly escorted enemy convoy which is in the process of being attacked by a friendly destroyer, a squadron of friendly torpedo boats, a couple of artillery barges and a few Stuka dive bombers for good measure.
It isn't a particularly challenging mission, but it is so much fun because you feel like you are just one of the pieces in a larger battle, and you get to sink ships with lots of crazy mayhem going on around you.
Goodluck with your mission pack, I'm looking forward to it.
edit: I forgot to answer any of your questions
- About an hour or so is good for me. Some of the fun missions in GWX/Stock you can complete in much less time than an hour. In general I'll play a patrol if I want a long game, but if you are gonna make 5-10 missions a mix of quick and longer battles might be a good idea.
- I dunno, I've never played SH3 online.
- I prefer English.
- Depends. Sometimes as short as 20 minutes, sometimes as long as 4 hours at the weekend.
- No preference for me.