how to determine whether I have 64bit or 32 bit node executable installed?

Run this from the command line:

node -p "process.arch"

It will return 'arm', 'arm64', 'ia32', 'mips','mipsel', 'ppc', 'ppc64', 's390', 's390x', 'x32', or 'x64'.

https://nodejs.org/api/process.html#process_process_arch