HW 4.1
Your K's should be about Kaxial = 1.7, Kbending = 1.6, and Ktorsion = 1.32.
Max principal = 42.55 MPa.
Be sure to check the bending stress at the wall.

HW4.2
Both factors of safety are near 1.

HW4.3
A.  NMSST = 3.61
B.  NDET   = 4.64
C.  NMSST = 2.25
D.  NvM   = 3.00;  This is a 3D stress case (XY stress circle doesn't cross the Shear axis, so one of the three principal stresses (in this case, the maximum) = 0.