" After your ship fires, it must set its course and move. You establish your ship’s initial speed during setup , and you must continue to move at that speed until you reveal a navigate command. Your speed determines both how far you can move and how many times you can click the game's maneuver tool to adjust your course at each speed increment"
Ah well spotted. It does imply that the initial speed you set can be anything (up to its max speed), but it is too vague to confirm it either way. I guess this is just one more thing we'll have to wait for the rules to see how it will work.
I don't see a problem with speed 0. As others have said, in an objective game sitting at the edge of the board is unlikely to be effective, but stopping near an objective to hold it might be. Remember these ships can't turn around easily so stopping will be necessary to control specific areas, but that does leave the ship vulnerable to attack.