Q1 - shouldnt be a problem as long as you're careful with which partitions you install
Q2 - yes - exactly the same
Q3 - you can do it either way - personally id format it from the windows 7 installer - that way you're less likely to foul-up the boot manager especially if you are already dual botting.
The general rule is to go from earlier OS to the later ones. So if you have your Vista and XP installs already set up, then you should be able to add 7 to a new drive/partition, do a startup repair, and see all three.