1 Both are correct. The second sounds as if the decision has been made earlier.
2 This is correct in British English, but I have seen American speakers criticise the usage. In BrE, we use the future perfect for assumptions about actions that have been completed now.
He always gets home by 5. It's 5 now: He'll have got home by now.
3 Slight shift of emphasis. I think the first would be more common.
4 We often don't bother with the past perfect when the meaning is clear.