Welcome aboard!
One thing I'd point out when looking at CT task resolution is that there are very few modifiers. You can add skill level, add a bonus based on attributes (IIRC, take the attribute and divide by 5, rounding down: there's your DM) and not much else. I think this is the elegant simplicity of the CT system - the referee gets to decide how difficult a task is, and sets the task number (X+) to reflect that. The situational modifiers are built right in.
For example, let's say a 'typical' vehicle repair job, whatever that is, needs a 7+ to succeed. Add +1 for mechanical skill, and +1 for INT or EDU 7 (7/5= 1.4> 1) so you really need a 5+ to succeed. Pretty easy. But wait! What if the vehicle was built from sub-standard parts, or is poorly designed? Instead of needing a chart of modifiers for engine quality, the referee just ups the target number by a few, depending on how hard he thinks is should be. Now it's a 9+ to succeed. Harder, but still doable.
It will help the referee to have an understanding of percentage likelihood of a given number on 2D. The math is beyond my ability to do in my head, but for example, I think that an unmodified 12+ on 2D has an 8% of success. 7+ is pretty close to 50%. Of course, if a job is really hard you can set the task number at 13, 14 or higher so only the very skilled and very lucky can succeed.
Hope this helps.
Cheers,
Bob W.