In reading various forums, I had thought I was supposed to see Lame show up under the Effects menu in Plug-ins in Audacity, which it never did. I'm not sure where the disconnect was or where more information lies re: how to confirm a successful installation, but I was able to confirm that Lame was installed correctly by doing the following:
1. Creating a test audio file
2. Going to 'File'
3. Then 'export'
4. Then 'mp3' will be an export option
If you see mp3 as an option for exporting your file, Lame has installed correctly.
I learned that by simply opening Audacity and selecting 'File', then 'export', that the 'mp3' option is greyed out. You have to actually create an audio file, not just open one in order for the mp3 option to appear.
As for the ACX Check plug in, I was able to successfully enable that in the Plug-ins menu in Audacity after searching my computer for the 'hidden' library referenced above. I guess I somehow missed that there were two libraries with the same things in them so I kept dropping ACX in a folder that looked exactly the same as instructions described, yet it wasn't the right folder.
Thanks everyone who helped me complete these tasks.