From the screenshot, it looks like you forgot to do step 2 in my instructions above. The "(in Sketchbook)" suffix on the Tools > Board > Sanguino (in Sketchbook) menu item shows that it is still using the Sanguino boards platform that is installed under <sketchbook folder>/hardware/Sanguino, but I told you to delete that.
It does not. Arduino IDE 1.x and 2.x use incompatible configuration systems, with separate configuration files.
There should be after you follow my instructions above exactly.
Yes
Yes