1. Changing your facing is free as part of your movement. If you cannot move (say due to disruption) or if in the assualt phase you you opt to attack instead of moving then you cannot chnage facing.
2. Unless otherwise indicated on the card, all units can fire in any direction regardless of the facing. Units that have restrinction are noted on the card and usually state “Fixed Howitzer” or some similar special ability (or restriction as the case may be).