Sounds like a great project.
Have you considered cutting your maps up. That's how we generally do it.
This is Anna Meyer's world and a great example of how cutting it up can make it more manageable. Just link the pin to a topic that contains a more detailed map of that section.
I'm sure you could find a way to do the call. But in my experience I've had to host the files externally to Realm Works and then have Realm Works call them in a foreign application.
Realm Works is not the same as Fantasy Grounds. They are designed for different purposes. Personally I still use MapTools for example to show the players the maps on the table. If you objective is to just show the maps to the players I would recommend a VTT. Realm Works is better suited for documenting and mapping that world out in a way that makes it usable to you.
Personally I believe both applications have their place and purpose, in the way i run my games at least. All come's down to what you are trying to achieve.
