KISS on the rocketry stuff..... a centering ring for a router is two circles, fins are the outline, fancy things with lots of holes are just more circles. A 3D model is fun to look at but ALL of my parts production jobs are done with flat 2D CAD. Bevels could be carved, but they're usually a feature on both sides of a part and THAT requires flipping it in a fixture of some sort. A purpose built grinder or sanding fixture is much faster in the long term.
I use Vcarve Pro, there's another Vectric product called Cut2D which is mostly CAM but a little bit of CAD, it's designed to import 2d vector art and provide tool path outputs. Cut2D is pretty affordable, there are freebie vector drawing packages.
In VCarve Pro there's an add on widget that imports .CSV files into vectors- that's something you can do in Rocksim- in the fin design dialog there's an export option, with CSV as one of the formats. Almost never imports as a closed vector though, the root edge is usually missing. I draw the fin shapes out of OR or Rocksim using the coordinate pairs list in the free-form fin dialog.... if fins are drawn as trapezoid style, I use the convert to free-form and then use the coordinates. It's quick to redraw that way.
Here's an example of a nosecone bulkhead and mount for a 5" wound cone/coupler setup. On the right- the 4 larger circles were distorted into slight ovals and then the overlapping vectors were trimmed back to make the mount piece. Note that the lid/plate vectors were included in that drawing as well, including the small holes which are clearance for #10. They'll be spotted with the 1/8 endmill and then drilled out, easier to get good holes that way. Stack up the parts, everything will line up, then peel them apart into separate components. The ability to trim vectors is very useful.