So, my SD has Speed 1 but overlaps a corvette when moving, the ship is now -1 'temporarily' so is at speed 0.

1- For incoming attacks can the SD use defensive maneuvers?

2- Is it's Speed dial turned down to 0?

Your speed is only reduced temporarily during the move. It is still 1 when being attacked and for future movement. Page 8 RRG, under 'Obstacles'.

The speed dial is not turned. The speed is only changed for this movement action, so you can use your Defense tokens afterwards.

Cheers, must remember to check the RRG