I find out a bit more info by experimenting.
A slightly more efficient way to rough the cylinder (cutouts) is to use bounding curves for the machining (region curves). You can add, for example, six individual region curves all the way around, and then let Madcam machine each region in succession.
This is to minimize wasted cutting in free space (due to Madcam trying to rough a bar shape when using an unbounded roughing pass). A single yellow region curve is shown below which bounds a single 3d roughing operation below.
A good feature to add would be the ability to define cylinder shape stock, or define stock shape from model.
While I am requesting things, part tabs would be nice too. For 2.5D contouring of thin sheet, I think the best way to currently handle this is to trim out segments in your contour (Rhino 3D trim). This is pretty easy. But if you are contouring at multiple Z depths, it becomes more complicated to implement.