Sounds like a good find. I have owned a 1980 300SD for 8 years and it has been very enjoyable.
CC may be an easy fix or not. If not, replace the unit with a Rostra electronic or similar. Retain you current CC control switch.
Don't have a sunroof so can't respond on that.
Brake lines are not expensive and straight forward to replace.
Driveshaft cover should not pose a problem. Had mine off once and it's thin steel if I remember correctly.
Watch the HVAC unit under hood. It can fail and leak. I replaced mine with an Unwired unit and never have had anymore problems.