1)
Why does it say "v'Al Te'asher [b'Derech Ra'im]"?
1.
Rashi: Do not go on the path. Te'asher is like "ba'Ashuro Achazah Ragli" (Iyov 23:11), "v'Arum Yavin la'Ashuro" (14:15).
2.
Malbim: Derech is a great intercity road. Orchos are small paths that branch off from the Derech to towns and villages. Resha'im do evil deeds. Ra includes one who is evil, even if he does not do evil acts, e.g. a heretic or Apikoros. His evil is in heretical thoughts and denial. Every Rasha has his special path on which he goes to do evil. This one goes to murder, and this one to adultery, theft
