You can set the duct length and have it break into sections of that length by checking Specify cut length on the design tab of the property palette in the Dimensions section at the bottom. AutoCAD MEP will not automatically insert couplings.
If you are using AutoCAD MEP for sheet metal detailing then be prepaired to create alot of custom content. There is no real world equipment in the program and most companies do not provide this equipment. They instead provide revit models. Because of this I am in the process of placing my manufacturer specific equipment up on the AutoCAD MEP App Exchange website. I am undecided if i will charge a small fee for the equipment or not as of yet. If i do then it will not be more than $.99 for each family of equipment where a family would include a size range. For instance the Titus DESV VAV Box part would contain all sizes of the part.
Because of the App Exchange policies it will take me probably another month or so to start getting these uploaded. That is because they require that they be automatically inserted into catalogs and working as soon as you start the program. This requires some custom programming to get this done.
You might have a look at www.eccadcam.com. They offer an addon package for AutoCAD MEP that includes automatic downloading to the Vulcan software. In other words you can take your design in AutoCAD MEP and create a pickoff drawing that can then be downloaded to the vulcan software. It requires very little human input once the design is complete.
