I have updated Freemarker Plugin to :

1) have template completion capability : (ex : type list in your ftl template, and CRTL+SPACE => <#list ....><#list> will be generate.
You can customize your template with menu Window/Preferences/Freemarker Editor/Templates

2) add XML context capabilty. You can choose XML file and have completion with element and attribute of your XML.

3) add String context. I beleive it will be better to have Java Type context (Boolea, String,...)

3) add Preview Tab to see the result of the merge of your template and your model. It works ONLY with XML context. It's not available dor Class context.
To use Preview Tab with Class, I believe it will good to have a class wich return getter of your Class.
Ex : if you have class MyForm, user will have to add getMyForm in the context class for the preview.

MyForm getMyForm()

{ MyForm form = new MyForm form.setId("MyId") return form; }

If user have the ftl template ${myForm.id}, when you click to th epreview tab, you will have MyId displayed.