How best to distribute an add-on
 

What is the best-practice method to distribute and have people add a one-piece add on to their UI? Its just one custom Page - It would be fine if they had to make a macro that said /show_page Custom.Whatever in order to use it..

So basically hwere is the universal place to put this so that it would work regardless of what other UI stuff they have installed..

Have them add an <include> line to eq2ui_custom.xml if they already have one from another mod or otherwise provide a sample eq2ui_custom.xml that they can use.

To let users open it use the macro idea you proposed or maybe add it to the start menu. A while ago there was an effort to make a standardized start menu framework (link) but it was never quite completed.