Do not understand the first question.
If you mean H1-transfer.
1. You can start work for new employer right after receiving the receipt for H-1 transfer
2. The old H-1 automatically ends when you leave the old sponshor.
3. Yes, you can do that, But it seem stoo short. Your intent working for the first company will be questioned. You may have problem with H-1 transfer and h-1 visa application in the future. Give it three months.
If you mean H1-transfer.
1. You can start work for new employer right after receiving the receipt for H-1 transfer
2. The old H-1 automatically ends when you leave the old sponshor.
3. Yes, you can do that, But it seem stoo short. Your intent working for the first company will be questioned. You may have problem with H-1 transfer and h-1 visa application in the future. Give it three months.