If you have your extrusion vector and one reference vector you can cross multiply them to retrieve your 2D planes' right vector in 3D space.
I usually use the global up
vector as my reference. So your extrusion
vector cross multiplied with global up
will result in a local right
vector. Another cross multiply between your extrusion
vector and your new local right
vector will result in a local up
vector.
Once you get both your local right
and local up
vectors, those will be your planes X
and Y
vectors in 3D space.