Hello there, Paul! Thanks for getting in touch–we’re stoked to hear you’re looking to go PRO. 🙂
Yes, Custom Fields are compatible with the calendar but, like other WordPress templates, you may need to specify directly where they display in the template. We have a Themer’s Guide that walks you through the ins and outs of customizing calendar templates for things just like this.
This isn’t PRO-specific, so if you already have the free version of the calendar, you can test your work there. Might be nice to test drive that feature, but I also want to let you know we have a full 30-day refund policy if things don’t work out when you go PRO.
Does this help answer your question? Please let me know.
Cheers!
Geoff