Reporting back a year later -- Among the problems here, (1) the project should never have been build as a console app; WSTP programs should be built as Win32 apps, and (2) I was including all sorts of libraries that I didn't need. Only wstp32i4.lib was needed. I have created a number of useful WSTP since.

I don't think that's it; I have copies of the DLLs in the binary directory. Without them, the binary won't run when double-clicked upon but with them, it runs then crashes. The behavior from within Mathematica seems to mirror the behavior with the DLL in place, so it looks like the system is seeing the DLL.