You can have up to 6 secondary accounts in addition to your Primary. Here are the instructions-------
As for the Avatar, you would normally change it in your forum profile. But I think you have to get in a certain number of posts before you can access the tool for that.
You also have the option in the new email format of using the "mail fetcher" feature. In the folder pane click on "Add mail account", and you can enter as many external accounts as you want, including any secondary Comcast accounts you have. Not quite the same thing as a desktop client like Pegasus, but useful all the same if you only want to work in the webmail UI.