Paraphrase:
Yes, keep overnight in pen with straw and only water, no food. They will eat a bit of the straw but not enough to matter.
Hanging will probably be for a week (or Monday to Friday), no need to ask for specific, they will do the reasonable thing.
Butchery, several options, good idea to ask for lots of variety, small cuts (although with Shetlands that's not really an issue). Option for individual vac pacs costs a little more but is easier to manage than getting one big sack of meat.
Best way to tell which meat came from which sheep is by weight, the meat will be in per sheep batches but not labeled by ear tag -- so weigh them before they go.