Hi William,
Welcome to OpenACS.
#1. I assume that have OpenACS 4.5 already installed since you are already trying out e-commerce. You can go to http://youroacs/doc and read the other installed packages there. You can also grab this yucky patch https://openacs.org/sdm/one-baf.tcl?baf_id=1602 so you can read the uninstalled packages too. You can start with ACS templating.
#2. Nope Red Hat will not bother OpenACS. The short history of OpenACS 4 (not including ver 3). Is that Arsdigita (now acquired by Red Hat) stopped the development of the Tcl version. OpenACS community picked it up and made it better. Hence OpenACS is the only Tcl child of ACS. CCM is the Java child of ACS. Red Hat is only doing CCM. Since you are a Tcl nerd it is best to start with OpenACS, CCM is also ok if you come from a Java background. Therefore OpenACS is the best place to be if you are developer of OpenACS and ACS.
We hope you will enjoy your stay with the community.