It's a fairly steep learning curve. So I recommend not doing the traditional "dive right in and start hacking" but rather some patient reading and learning the language and SDK first -- it will pay off.
Work through a tutorial on the Lua language: lua-users wiki: Lua Tutorial. It is a very simple language, but in practice being productive with Lua is much different than with other more traditional languages. Investing a couple of hours learning the language first will save you lots of grief down the road, especially considering the near-complete lack of built-in debugging facilities in LR.
Install Lua 5.1.4 to get a standalone Lua interpreter for learning the language:
Mac: Command-line interpreter binaries here: LuaBinaries - Browse /5.1.4 at SourceForge.net
Download the LR SDK. It contains the "Lightroom SDK 6 Programmer's Guide", which provides a detailed introduction to the SDK. Spend some time familiarizing yourself with the entire SDK. The SDK also includes source code for the Flickr publishing-service plugin.
Either get my debugging toolkit or find the post in this forum that talks about how to connect a particular IDE's debugger to LR. The debugging toolkit is lighter weight but more limited in capability. If you try to debug using just print statements, you'll soon end up spending many hours in frustration, given how limited the LR execution environment is.
Thank you for a very well written and thorough response. I was hoping to "dive right in" as you say but after trying that approach for a short while I had decided your advice is solid. Short of Jeff Friedl giving me a copy of his code. I think this answer fully satisfies my question.