Started with the R for Mac OS X FAQ, after a quick perusal of this item on Sierra and R. That document appears to argue that I should stick with Yosemite (Mac OS X 10.10). The Mac OS CRAN archive appears to only have versions for Mavericks (10.9) and El Capitan (10.11), but not Yosemite (10.10) or Sierra (10.12). Here’s the problem with Yosemite.
I may have to revisit that info, as well as one idea or another about using Homebrew for the installation (and maintenance, I suppose).
For the next step, though, it’s on to review the NetLogo R-Extension, and explore it a bit with this tutorial, watching out for issues, such as those in this troubleshooting guide.