Hey... I'm an experienced duper. Can dupe about 100 ammies + if I do it the whole day.
1. No, it doesn't matter, but in some cases, it does help.
2. No, it's not necessary, I use CTRL + W in Google Chrome and it helps.
3. No it doesn't.
How I dupe
Once one client is hanging and the other is in the vault, drag your items into your inventory. Once you've done so, get CTRL+W ready. As soon as it says connected it should work. There's always a big chance it won't work. If you need any more advice send me a notification.