TPH,
For some one who doesn't know what they are doing, you seem to be doing all right? Nice work.
I read your post late last night and was going to reply this morning, but you got there first. I'm not quite sure what the 'hide if invalid' set to false does, as I normally use that for troubleshooting shipping problems, but hey if it works...
To summarise, the freeshipper module should cause all other shipping methods to be hidden, if the cart products have the 'always free shipping' selected, and/or have a weight of zero.
The weight is a point of debate, as the store shipping/packaging configuration cas cause it to add a packaging weight even if the product weight is zero, and perhaps that is what the 'hide if invalid' is doing?
The other contentious area to test is when you have a 'mixed' cart of some free and some not, to check that the shipping, tax etc are being correctly calculated.

Chuck