You can make a custom component by creating a new “Custom HTML” form, deleting all the components, and editing the html property. You can then drag that form onto other forms as a custom component (drag it from the App Browser on the left into the page).
As for parameters in the URL, you can see David’s question on this forum today.
For more than that, I think you’ll have to consult the Facebook API docs! If you really need to generate a static HTML page, you can use our HTTP API, but I’d suggest that as a last resort.