whpalmer4's approach is much the most flexible and powerful. The nearest thing to your first draft that AS itself could understand would be along the lines of:
Code:
tell application "OmniFocus"
tell default document
set Val1 to "foo"
set dteNow to current date
make new inbox task with properties {name:Val1, due date:dteNow + 1 * days}
make new inbox task with properties {name:Val1, due date:dteNow + 3 * days}
make new inbox task with properties {name:Val1, due date:dteNow + 7 * days}
end tell
end tell