Hi Brad,
I want to confirm what you are aiming to do; do you want to mount the same adf file all the time (in which case the startup sequence can be edited to do that)? With a vanilla OS3.2 install simply double clicking an adf icon should mount it, but from your second question you appear to be mounting them already.
Re: read only files, single click the adf icon and right click to bring up the menu and look at the information for the adf. There is a tooltype 'writeprotected=no' but it's commented out with brackets by default. Remove the brackets and save and the disk should become read/write when mounted (just tested on my OS 3.2 setup with a couple of random adf files).
Lastly, great that you are online with your A1200. How did you do it in the end after your problems with plipbox and then the pcmcia card you tried?