RE: Officer attendance at scrutiny meetings
I think that in practice it depends on what you're trying to achieve, but in the constitution it should say "Chief Officer" or "Executive Director" or whatever title you give your most senior management level. You can always add "or their nominated representative" if you want to give a little wiggle room.
Generally, I think you would always suggest that the Chief Officer attends, usually with the Cabinet Member, and let them decide if they want to bring along the service expert to help them with the tricky technical bits. Depends a bit on the size of your organisation as well, though, and bigger councils might want to drop the requirement down a level or two