Is it common to have mild trochanteric bursitis, sacroiliac degenerative arthritis and l5-s1 facet arthropathy? What is indicated by this combination?

May be may be not. Multiple joint pain inflammation may be related to an underlying auto immune arteritis or totally independent factors causing pain in different joints. Certain blood tests may help to determine , mist if the time treatment may be the same, antiinfalmatory , physical therapy, posture and life style modification .
Yes. Many times these are found in normal people. Unless it bothers you i would not be concerned. If you are in pain and conservative care is not helping consider specialist referral.
Arthritis. Probably you have o.A to watch for other problems.