1. Well, as I've read and tested in printers using bowden to guide filament from extruder to printcore 4mm of retraction is a point when retraction starts to happen. This happens due to a tension in bowden tube, and retraction of 4mm just lower the tension. In UM machines retraction should have greater values.
2. I agree that travel move should be fast enough to break oozing material, but in some cases printers use Z-Hop, and travel happens after leaving a blob. If You guys use it, try to turn it off.
3. I agree as well, good way to set up temperature is to print an object few times while lo