I see that when using an iframe, the fotomoto shopping cart is disabled.
Yes. This is noted in the 'Using an iframe' support section here.
Is this the case also when using custom purchase URL's?
Yes. Unfortunately, all shopping cart functionality is disabled when a gallery is loaded into an iframe.
Rather than use a web template site (which would require that you host the gallery elsewhere and load it into an iframe), you could perhaps sign up for some web space with a regular web host so that you could upload web pages with Juicebox galleries embedded directly into them.
There are many web hosts which offer free web space which would be suitable. Try a web search with terms such as 'free web hosting'. Please be aware, though, that with a paid account, you will likely better support, greater stability (less downtime) and more features.
If you did have your own web space, then you might like to consider another one of our products - Showkase.
Showkase is a PHP web application which would allow you to create a complete portfolio web site online using a web browser interface.
Showkase has full support for Juicebox-Pro (including Social Media Sharing, Search Engine Optimization, Fotomoto support and the ability to enter individual purchaseURLs for each image via the interface) and the galleries can be created within the application itself (or created with JuiceboxBuilder-Pro and then imported into Showkase).
Showkase also has the ability to create non-gallery pages such as 'About', 'Contact' and 'Basic' pages where you can enter information about yourself and contact details.
Demo sites created with Showkase can be found here.
All of this is done automatically within the Showkase interface without the need for any manual coding at all.
If you would like to take a look around the Showkase interface, you can log into the Live Demo Admin here.
Showkase can be purchased as Showkase-Standard (which comes with Juicebox-Lite and SimpleViewer-Standard, the free versions) or Showkase-Pro (which comes with Juicebox-Pro and SimpleViewer-Pro). The only difference between Showkase-Standard and Showkase-Pro is the bundled viewers.
As you already have Juicebox-Pro, you could purchase Showkase-Standard and upgrade it to use your Juicebox-Pro files by following the instructions here.
could you have the SEO option ticked, captions entered and the caption set to use none?
Yes. You can enter captions for your images, select the 'Add SEO Content' checkbox (so that the captions are used in the SEO content) and set captionPosition="NONE" (so that the captions are not displayed in the gallery).
I set the captions to "use none" so they would not display under my image however they do appear.
Please make sure that your gallery uses Juicebox-Pro and not Juicebox-Lite. captionPosition is a Pro only configuration and is not available in Juicebox-Lite (the free version).
Also, try clearing your browser's cache before reloading your gallery's web page to ensure that your browser is fetching and using the most recent versions of your gallery files from your web server.
If this still does not help, then please post the URL to your gallery's web page so that I can take a look and help further.