1) The form builder wizard creates entire forms, but there are many underlying server behaviors that can be used individually. To add CAPTCHA to another page, copy and paste the CAPTCHA fields from an existing form builder page and update the Sever Validation to validate the CAPTCHA fields.
2) I will log this as a bug to be addressed in the next dot release.
3) We will be addressing the creation of simpler forms in several ways. The current complexity reflects the complex design options that are available when configuring a design. We understand the trade-off between flexibility and complexity, and do intend on creating tools that will better integrate into existing forms.
4) The update functionality of form builder should only be used if you haven't edited the form html or css by hand. The best way to handle this is to create a separate .css file that can override the css in form-builder for any .css tweaks you want to make by hand. That way when form builder updates it's css file it won't interfere with your updates.
If you have edited the html by hand it is probably not a good idea to re-enter the Form Builder Wizard since it will be overwritten. But if you are customizing the html you would probably want to use your own custom format, so you should be able to copy and paste and update field names using your edited html.
The main issue with the form is that the CAPTCHA isn't working. It looks like GD is working, but no text is displaying. So it is most likely an issue with the font file.
When it works you will see the CAPTCHA at: wavt_captchasecurityimages.php
That file never changes, so if it doesn't work on this page it won't work on any page. I think the issue may be that you haven't uploaded the /webassist/captcha/font/ folder. I get a 404 when I try to view: monofont.ttf