OK, I looked around but didn't find much on MPP 1.6.6. Is this the recommended version? All of the threads I have seen recommend 1.6.5d, but it is probably because they are from before 1.6.6.

It looks like the installation is 1.6.5b (BTB Edit), remove the .esp, add 1.6.5d (requires data files from 1.6.5b), finally, add .esp for 1.6.6 (requires data files from 1.6.5b and .esp from 1.6.5d).

Is all of that correct?

Thanks in advance!

You almost have it correct. Get the resources (meshes, textures,etc,) from 1.6.5b and the esm from 1.6.6. You don't need 1.6.5d at all. The 1.6.6 esm replaces all prior esm files, so delete the 1.6.5b esm and use the 1.6.6 esm instead.

Edit: also, look for a new and improved version in one complete package in stores soon!

Corrected for you.