for a trailer if you have a good enough imagination one can do all by themself.
Flyby's are nice, combat is good, but what is it you really want to portray will dictate what you need and how many will be needed.
Say for instance you take a Cap ship and gun boat on patrol, then would be best for 2+ people to be involved.
If you want the rogue character that stumbles onto something, 1+ person/people can be used.
other alternatives, find an NPC patrol group and get some shots with them.
ok technicals:
vid size of 320x480 is OK (bout that) youtube and all else use cause it keeps MB sizes low
640x480 standard TV resolution and old monitor display settings. also default on lots of intro vids to games.
-----do note that 90% of all vids hanging around are about this resolution.
LARGER resolutions= VERY GOOD. they are large files to dl and share, however you can put in as much detail as you want.
Sound quality= 2 channel. Even if you have a sound editor that can excede more than 2 channels it is pointless as 75% can not hear the extra or is drowned out by the front two, or like me have headphones on so I can listen to anything as loud as I want.
Please normalize your sound track to the video, typical thing most forget to do then you have scenes louder than others and music blasting at wrong parts etc.