I'm not sure if it is in the documentation other than reading the Ace3 code, so here's a tip: if you create the toggle mentioned above in your options table, you can set the load state as per user settings.
Lua Code:
function MyAddOn:OnInitialize()
-- set up your saved variables and defaults as normal for Ace3
-- keep user setting for enabled/disabled
self:SetEnabledState(self.db.profile.enabled) -- this line, assuming you name the toggle enabled in the defaults table
end