Just purchased the plugin.
I want to add it to a running site.
Is there any risk of breaking its functionality or design?
Are there measure I should take?
Only when you explicitly set something up in Toolset that you would expect to affect the design should it do so (for example, you create a new template to control the appearance of posts of some custom post type).
It's a sensible precaution though to take a current backup before you start working on changes to your site.
Thanks for your reply. I'll assume the ticket from here.
When you say 'instances', what exactly type of content are you referring to?
Regarding the second question, yes, we have several demo sites that you can use to be the basis of your projects. Please check our discover wp program: