1. Seeing as how you are new to this, I'd recommend not foiling. They'll be fine! I always use the bend test.
2. 250 is fine.
3. Untrimmed spares can take up to 5-6 hrs.
4. If you finish early, you can wrap'em so they'll stay warm. If you finish them right at eating time, you can just cut them up and serve.
UDS, mini wsm, 22.5" weber kettle