Building a form with several scroll panels

Scrolling panels is definitely the way to go. I wouldn't use drop-downs because they are time savers chiefly when the same choice needs to be made in several locations. Otherwise, they take a lot of effort to implement.  With a scroll panel, all you have to do is to create the object, and drag it into the panel.  When the contents exceed the size of the panel, it automatically adds the scroll bar. That means you can create panels one line high, that look like blanks in a form, but can contain hundreds of options. I envision something like, for example, a panel for size, one for material, one for power source, etc. 

Then you need:

1. Three variables - size, material, and powerSource

2. Inside the power source panel, hundreds of options. each option would be a separate text box, with its own triggers. Sometimes it is easier to create and complete the object, and then move it into the panel. If you want graphics you can use them instead of text boxes. If you want both, you can put the graphic in the hover state of the text box. (Put it to the side, so it doesn't cover other choices.)

3. For each choice, create a trigger: "Set variable powerSource to "12 volt dc" when user clicks text box - 12 volt dc". 

The variables retain the chosen option, and make it available anywhere in the project that you need it.